CLI: --strict, and a warnings array in result.json (#14601)

# Description

Add `--strict` for CI and scripted pipelines, and a structured
`warnings`
array in `result.json`.

## `--strict`

A NON_CRITICAL slicing warning is logged and the slice succeeds: return
code
`0`, G-code written. That suits interactive use, but a pipeline then
ships a
slice with a warning nobody saw. With `--strict`, such a warning fails
the run
with `CLI_SLICING_ERROR` before the G-code is exported. Without the
flag,
nothing changes.

In FFF the warning that reaches this path is "support needed but
disabled"
(`PrintObject::generate_support_material`). `--no-check` skips that
check, so
`--strict --no-check` is rejected with `CLI_INVALID_PARAMS`.

`--strict` is read before any work, so it doesn't depend on argument
order and
`result.json` reports it for early failures as well.

## `result.json`

Two new top-level fields:

- `warnings`: `[{"class", ...details}]`. One class is wired:
`slicing_warning_non_critical` with `plate_id` and `text`, recorded
whenever
such a warning fires, with or without `--strict`. The array also fills
on
  runs that succeed, so `return_code` stays the verdict.
- `strict_mode`: whether `--strict` was on.

`record_exit_reson` writes `result.json` on Linux only, so both fields
exist
only there. The non-zero exit works on every platform.

## Tests

- `tests/fff_print/test_support_material.cpp` (all platforms): an
overhang
sliced with support off raises the NON_CRITICAL support-needed status,
and
  the no-check flag suppresses it.
- `tests/cli/test_cli_strict.sh` (Linux only): runs `orca-slicer`
without
flags, with `--strict`, and with `--strict --no-check`, and checks the
shell
status and `result.json` of each. It runs the built binary, so it
carries the
`RequiresApp` label, which `scripts/run_unit_tests.sh` excludes because
the
  unit-test job only receives `build/tests`. Run it with
  `ctest --test-dir build/tests -C Release -L RequiresApp`.
- CI: `unit_tests.yml` now passes `Release` on Linux too.
`build_linux.sh`
configures Ninja Multi-Config, and without a config ctest drops the
labels of
plain `add_test()` tests, so this test ran as "Not Run" instead of being
excluded. The docs that assumed Linux was single-config are corrected
too.

Built and run locally on Linux (GCC 14) on current `main`: both tests
pass,
and the touched files compile clean under Clang with `-Werror`.

AGENTS.md

@@ -20,9 +20,9 @@ cmake --build . --config %build_type% --target ALL_BUILD -- -m
 Catch2 framework. Tests in `tests/`; see [tests/AGENTS.md](tests/AGENTS.md) for where a new test belongs and the conventions to follow.
 
 ```bash
-cd build && ctest --output-on-failure           # all tests
-ctest --test-dir ./tests/libslic3r              # individual suite
-ctest --test-dir ./tests/fff_print
+cd build && ctest -C Release --output-on-failure    # all tests
+ctest --test-dir ./tests/libslic3r -C Release       # individual suite
+ctest --test-dir ./tests/fff_print -C Release
 ```
 
 ## Documentation