feat(imex): polish UI per PR feedback + add parallel-mode safeguards

Felix14-v2 PR review feedback (https://github.com/OrcaSlicer/OrcaSlicer/pull/13086#issuecomment-4323696312)
plus the slice-time validation work that follows from his bug list.

UI polish:
- Capitalize "Primary" in display (right-click mode menu, plate tooltip).
  Sentinel stays lowercase for wire compatibility.
- Pre-slice-warnings checkbox now uses Orca's ::CheckBox so it matches the
  green toggle style of the rest of the IDEX/IQEX configuration page.
- DPI-scaled the IMEXModesCtrl (modes editor) sub-panels, button grid,
  text wraps, gcode textarea, and the ghost-tooltip swatch (imgui.scaled).
  Legend swatches sized to body-text height for visual balance.
- Primary mode tool buttons in the modes editor are now disabled (read-
  only): cycling roles on the IMEX-off mode is a no-op and confusing.
- Modes editor sub-panels now explicitly inherit the app's window-default
  dark colour so chromeless ScalableButtons don't render with a visible
  light box around their icons on GTK dark themes.
- Per-mode-line reset arrows in the modes editor: each row gets a small
  reset bitmap that snaps that row's name+tools+gcode triplet back to the
  saved preset's value. matches_config() guard on the page-level reload
  prevents the textbox-being-typed-into from being destroyed mid-keystroke.
- New View menu item "Show IDEX/IQEX Toolhead" — toggles the per-carriage
  footprint boxes during G-code preview playback. Gated to Preview tab +
  IMEX printer; backed by app_config so it persists.

Coordinated config migrations:
- imex_tool_layout and imex_viz_theme migrate from coString to coEnum
  (ImexToolLayout / ImexVizTheme). Existing wire format preserved so
  saved presets and 3MFs deserialize unchanged. Side-benefit: both now
  pick up standard Field rendering and so finally show reset arrows.

Slice-time safeguards (the validation half):
- imex_suppresses_bare_toolchange(parallel_mode, count): suppresses the
  slicer's bare T<n> at print-start in any IMEX parallel mode (the user's
  imex_mode_gcode + machine_start_gcode owns tool activation there). Mid-
  print T<n> emits normally — Print::validate blocks the configurations
  where mid-print T<n> wouldn't make sense. Applied to both code paths
  inside GCode::set_extruder (the long multi-extruder path AND the
  single-extruder path that fires when multiple_extruders=false).
- imex_multicolor_block_reason(): hard-stop validator returning a user-
  facing reason string when the active IMEX configuration can't physically
  support multi-color. Catches IDEX (1 tool/gantry), 2-tool-active IQEX
  (no within-gantry swap topology), and any MMU/AFC lane sharing among
  used filaments. Wired into Print::validate as a slice blocker, and into
  PartPlate::has_imex_multimaterial_conflict so the plater badge agrees
  with the slice block (no more false positives where the badge warns but
  the slice goes through).
- New imex_mode_types config option (parallel array to imex_mode_names)
  and imex_mode_type_for() helper. Mode-type tag drives behaviour: zones,
  ghosts, and validation interpret modes differently per type. Initial
  types: "primary", "copy", "mirror", "split". Split modes are explicitly
  designed for paired-gantry IQEX multi-color and bypass the gantry-pair
  check in imex_multicolor_block_reason (MMU sharing still blocks them).

Test coverage:
- New unit tests cover imex_suppresses_bare_toolchange (4 cases),
  imex_multicolor_block_reason (8 cases including IDEX, IQEX 2-/4-tool-
  active, MMU sharing, missing primary, Split type), and imex_mode_type_for
  (3 cases including legacy fallback). Total: 186 IMEX assertions across
  71 test cases, all passing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/libslic3r/PrintConfig.cpp

@@ -543,6 +543,24 @@ static const t_config_enum_values s_keys_map_FilamentMapMode = {
 };
 CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(FilamentMapMode)
 
+// IMEX: keep the legacy hyphenated wire strings so existing presets / 3MFs
+// deserialize unchanged after the coString -> coEnum migration.
+static const t_config_enum_values s_keys_map_ImexToolLayout = {
+    { "front-left",  int(ImexToolLayout::FrontLeft)  },
+    { "front-right", int(ImexToolLayout::FrontRight) },
+    { "rear-left",   int(ImexToolLayout::RearLeft)   },
+    { "rear-right",  int(ImexToolLayout::RearRight)  }
+};
+CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(ImexToolLayout)
+
+static const t_config_enum_values s_keys_map_ImexVizTheme = {
+    { "standard",      int(ImexVizTheme::Standard)      },
+    { "deuteranopia",  int(ImexVizTheme::Deuteranopia)  },
+    { "tritanopia",    int(ImexVizTheme::Tritanopia)    },
+    { "high_contrast", int(ImexVizTheme::HighContrast)  }
+};
+CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(ImexVizTheme)
+
 
 //BBS
 std::string get_extruder_variant_string(ExtruderType extruder_type, NozzleVolumeType nozzle_volume_type)
@@ -5561,13 +5579,22 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionInt(2));
 
-    def = this->add("imex_tool_layout", coString);
+    def = this->add("imex_tool_layout", coEnum);
     def->label = L("Tool 0 Corner");
     def->tooltip = L("Physical corner of the bed where tool T0 (index 0) is located. "
                      "Determines how tool indices map to bed zones. "
                      "front = lower Y (near the operator), rear = higher Y (back of machine).");
     def->mode = comAdvanced;
-    def->set_default_value(new ConfigOptionString("front-left"));
+    def->enum_keys_map = &ConfigOptionEnum<ImexToolLayout>::get_enum_values();
+    def->enum_values.push_back("front-left");
+    def->enum_values.push_back("front-right");
+    def->enum_values.push_back("rear-left");
+    def->enum_values.push_back("rear-right");
+    def->enum_labels.push_back(L("Front-left"));
+    def->enum_labels.push_back(L("Front-right"));
+    def->enum_labels.push_back(L("Rear-left"));
+    def->enum_labels.push_back(L("Rear-right"));
+    def->set_default_value(new ConfigOptionEnum<ImexToolLayout>(ImexToolLayout::FrontLeft));
 
     def = this->add("imex_nozzle_clearance_x", coFloat);
     def->label = L("Nozzle Clearance X");
@@ -5594,11 +5621,20 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionFloat(0.0));
 
-    def = this->add("imex_viz_theme", coString);
+    def = this->add("imex_viz_theme", coEnum);
     def->label = L("Visualization Theme");
     def->tooltip = L("Color theme for IDEX/IQEX bed zone visualization. Choose a colorblind-friendly theme if needed.");
     def->mode = comAdvanced;
-    def->set_default_value(new ConfigOptionString("standard"));
+    def->enum_keys_map = &ConfigOptionEnum<ImexVizTheme>::get_enum_values();
+    def->enum_values.push_back("standard");
+    def->enum_values.push_back("deuteranopia");
+    def->enum_values.push_back("tritanopia");
+    def->enum_values.push_back("high_contrast");
+    def->enum_labels.push_back(L("Standard"));
+    def->enum_labels.push_back(L("Deuteranopia / Protanopia (red-green)"));
+    def->enum_labels.push_back(L("Tritanopia (blue-yellow)"));
+    def->enum_labels.push_back(L("High Contrast"));
+    def->set_default_value(new ConfigOptionEnum<ImexVizTheme>(ImexVizTheme::Standard));
 
     def = this->add("imex_parallel_mode", coString);
     def->label = L("IDEX/IQEX Print Mode");
@@ -5631,6 +5667,20 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionStrings());
 
+    // Mode-type tag drives how zones, ghosts, and slice-time validation interpret a
+    // given mode entry. Parallel to imex_mode_names. Values: "primary", "copy",
+    // "mirror", "split". Empty / missing entries fall back to "primary" except for
+    // entries named "copy" or "mirror" (legacy compat with pre-type configs).
+    def = this->add("imex_mode_types", coStrings);
+    def->label = L("IDEX/IQEX Mode Types");
+    def->tooltip = L("Per-mode topology tag. \"copy\" / \"mirror\" produce one ghost per "
+                     "non-primary tool at the corresponding mirrored/copied position. "
+                     "\"split\" splits the bed in half along the gantry axis and aggregates "
+                     "each gantry's tools into a single multi-color print region — used "
+                     "for paired-gantry IQEX multi-color printing.");
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionStrings());
+
     def = this->add("manual_filament_change", coBool);
     def->label = L("Manual Filament Change");
     def->tooltip = L("Enable this option to omit the custom Change filament G-code only at the beginning of the print. "