MCP: scene.* namespace (CRUD by opaque object id)

[Grantim]

Summary

Adds scene.* MCP tools for domain-model access — read / write / add / remove / serialize by opaque uint64 object id (the raw Object* pointer, matching the ##<id> suffix in ImGui labels so ids are interchangeable between scene.* and ui.*).

Six tools:

• scene.listObjectTree — flat subtree dump keyed by rootId (0 = SceneRoot).
• scene.getObjectInfo — superset of one row plus childIds, worldBox, and the same info lines MI shows in its Information panel (plus the decomposed transform as text).
• scene.setObjectState — unified setter; any of name / visible / selected / transform is optional; multi-field calls wrap in one SCOPED_HISTORY so one Ctrl+Z reverts them atomically.
• scene.removeObject — detach from parent (subtree comes with it).
• scene.addObject — load from filePath OR {bytes (base64), extension, name}.
• scene.getObject — inverse: serialize one object via filePath (writes to disk, returns path) or extension (returns base64 bytes).

Shared infrastructure:

• New namespace MR::Mcp.
• New MRMcpCommon.h with skipFramesAfterInput (moved out of MRViewerMcp.cpp).
• New Schema::Bool in MRMcp.h.
• mcp VS filter groups MRViewerMcp.cpp, MRSceneMcp.cpp, MRMcpCommon.h.

All mutations push _t(...)-wrapped history entries via AppendHistory<T> — ChangeNameAction / ChangeObjectVisibilityAction / ChangeObjectSelectedAction / ChangeXfAction / ChangeSceneAction(AddObject | RemoveObject).

Test plan

Live-verified end-to-end via MCP against a local Debug build:

• Empty scene → listObjectTree returns [] (matches Scene panel).
• Cube created via ui.pressButton → listObjectTree returns 1 row; getObjectInfo returns 21 info lines (18 native + transform).
• setObjectState compound → all fields applied atomically; one Ctrl+Z reverts.
• addObject({filePath}) / addObject({bytes, extension, name}) → both load correctly.
• getObject({filePath}) / getObject({extension}) → both forms serialize; bytes round-trip through addObject.
• removeObject → scene shrinks; stale id → typed error, no crash.
• History panel shows MCP addObject / MCP setObjectState / MCP removeObject entries; Ctrl+Z unwinds.

🤖 Generated with Claude Code

[oitel]

This code might probably be moved to MRMesh as it's a common operation.

[Grantim]

Agreed in principle, but keeping DecomposedXf / decomposeXf / composeXf local to this TU for now — no second caller yet. Happy to promote to a MRAffineXf3Decompose.h in MRMesh the moment something else needs it.

[oitel]

I've missed the exception usage in MRViewerMcp but I do think we should get rid of them.

[Grantim]

Matches the existing handler pattern in MRViewerMcp.cpp, and the ToolFunc contract in MRMcp.h explicitly documents throwing as the error channel (/// Those functions are allowed to throw, that's how you report errors to the MCP.). I'd rather not change ToolFunc's signature mid-PR — happy to open a separate issue/PR migrating all MCP handlers to Expected<nlohmann::json> at once if we decide to go that way.