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/Print.cpp

@@ -1,5 +1,6 @@
 #include "Config.hpp"
 #include "Exception.hpp"
+#include "IMEXHelpers.hpp"
 #include "Print.hpp"
 #include "BoundingBox.hpp"
 #include "Brim.hpp"
@@ -1198,6 +1199,41 @@ StringObjectException Print::validate(StringObjectException *warning, Polygons*
     if (extruders.empty())
         return { L("No extrusions under current settings.") };
 
+    // IDEX/IQEX: block multi-color in non-primary parallel modes when the active
+    // configuration can't physically support it (no within-gantry toolchange path
+    // or MMU lane sharing). See imex_multicolor_block_reason() for the full rule.
+    if (m_config.is_imex.value && extruders.size() > 1 && !m_objects.empty()) {
+        const std::string& parallel_mode = m_objects.front()->config().imex_parallel_mode.value;
+        if (!parallel_mode.empty() && parallel_mode != kImexPrimaryMode) {
+            // Look up the active mode's tools string in the printer config's parallel
+            // table. Fall back to empty (block helper handles it gracefully).
+            std::string active_tools_str;
+            const auto& mode_names = m_config.imex_mode_names.values;
+            const auto& mode_tools = m_config.imex_mode_active_tools.values;
+            for (size_t i = 0; i < mode_names.size(); ++i) {
+                if (mode_names[i] == parallel_mode && i < mode_tools.size()) {
+                    active_tools_str = mode_tools[i];
+                    break;
+                }
+            }
+            const std::string mode_type = imex_mode_type_for(
+                parallel_mode, mode_names, m_config.imex_mode_types.values);
+            std::vector<int> used_filaments_0b;
+            used_filaments_0b.reserve(extruders.size());
+            for (unsigned int e : extruders)
+                used_filaments_0b.push_back((int)e);
+            const std::string reason = imex_multicolor_block_reason(
+                parallel_mode,
+                mode_type,
+                active_tools_str,
+                m_config.imex_tools_per_gantry.value,
+                used_filaments_0b,
+                m_config.physical_extruder_map);
+            if (!reason.empty())
+                return { reason };
+        }
+    }
+
     if (nozzles < 2 && extruders.size() > 1) {
         auto ret = check_multi_filament_valid(*this);
         if (!ret.string.empty())