Lights: Slice H — CLI/MCP parity, tests, docs

[fernandotonon]

Parent epic: #482
Depends on: Slices A–G (functionally requires A, B, C, E, G minimum)

Goal

Bring scene lighting up to project conventions: CLI, MCP, breadcrumbs, tests, docs.

Scope

• CLI — new qtmesh light subcommand:
  • qtmesh light scene.gltf --list [--json]
  • qtmesh light scene.gltf --add directional|point|spot --pos x,y,z [--dir x,y,z] [--colour #fff] [--intensity 1.0] -o out.gltf
  • qtmesh light scene.gltf --remove <name> -o out.gltf
  • qtmesh light scene.gltf --edit <name> --intensity 2.0 --colour "#ffaa66" -o out.gltf
  • qtmesh light scene.gltf --apply-rig three_point_studio -o out.gltf
  • qtmesh light --list-rigs
• MCP tools:
  • create_light(type, position, direction?, colour?, intensity?, range?, cone?)
  • delete_light(name)
  • list_lights() -> array
  • set_light_property(name, key, value)
  • apply_light_rig(name, replace_existing?)
  • All JSON-RPC on the main thread via QSocketNotifier; no BlockingQueuedConnection.
• Sentry breadcrumbs: scene.light.create, scene.light.delete, scene.light.duplicate, scene.light.rename, scene.light.edit, scene.light.shadow_toggle, scene.light.apply_rig, scene.light.gizmo_toggle, plus ui.action for menu/toolbar clicks.
• Tests:
  • LightManager_test.cpp — create/delete/rename/duplicate/find.
  • LightCommands_test.cpp — undo/redo for each command class.
  • LightRigLibrary_test.cpp — each rig produces expected light count + types.
  • MeshImporterExporter_lights_test.cpp — glTF round-trip.
  • Headless-CI safe (no real display assumed).
• Docs:
  • New "Scene Lighting" section in CLAUDE.md under Architecture.
  • Add qtmesh light examples to the CLI block.
  • Document the intensity-units mapping (QtMeshEditor scalar ↔ glTF lumens, FBX best-effort).
  • User-facing changelog note: "QtMeshEditor now supports multiple scene lights with presets, shadows, and full glTF round-trip."

Acceptance Criteria

• Every CLI subcommand listed works and supports --json where applicable.
• Every MCP tool responds correctly via stdio and HTTP transports.
• CLI ↔ GUI ↔ MCP parity: same operation produces the same result through every surface.
• Breadcrumbs emitted for every user-visible light operation.
• CLAUDE.md updated with the new section and CLI examples.
• CI green on Linux, macOS, Windows.

Effort

~5 days.