[bus 9d] Scenes and project domain: store-owned, routed through run

[HaD0Yun]

Part of #434 (plan v3).

Scope

Move the scenes and project domain onto the store. Line refs are at 793b4a4; after #460 the code lives in src/domains/scenes.js and the scene/project panels.

Store-owned state: scenes, activeSceneId (:2274-2275), scenesRef (read-only projection), projectName :4308, projectDirty :4309. projectHandleRef stays a runtime handle, off the document. Persistence keeps persistScenes to localStorage (:4277) and the .cclayproject file (:4500). None of this has undo today; scene add, rename, duplicate and reorder get one entry each.

UI writers through run (38 sites, App.jsx:12888 and nearby): scene add/rename/duplicate/reorder/switch/delete, project new/open/save/rename, export.

Semantic commands in src/commands/scene.js, src/commands/project.js, src/commands/export.js: the 6 registered scene/project actions plus the unrouted ones. Exposure follows plan v3:

• confirm: scene.delete, scene/project loads that replace the document (including the legacy load_scenes path, :5567), project.save when it overwrites a file (it needs user activation, :909), export.shotVideo, file pickers;
• open: everything that produces one retained undo entry.

Generic fields: add the scene kind to <kind>.set (name, order) and the scene list plus project metadata to inspect_studio document.

Depends on

• [bus 8] Pilot: stage domain store-owned, with generic set/read for stage #447 (pilot) store-owned stage and generic set/read

Files and concurrency

• Touches: src/domains/scenes.js (owned by this issue), src/commands/scene.js, src/commands/project.js, src/commands/export.js, src/commands/elements.js (adds the scene kind), src/scenes.js, src/project.js, test/bus/parity-pending.json, test/bus/verify-scene-commands.mjs.
• Domain migration: runs alongside at most two of [bus 9a] Shots and camera domain: store-owned, routed through run #441, [bus 9b] Objects domain: store-owned, routed through run #445, [bus 9c] Cast, prompt blocks and waypoints: store-owned, routed through run #442, [bus 9e] Motion and IK domain: store-owned, routed through run #448 (max 3 at a time). No other issue edits src/domains/scenes.js.

Acceptance

Each check is a red test(...) commit that fails, then a green commit that makes it pass.

1. The scene/project rows of the parity matrix, all origins x all checks: pending before -> green after, removed from parity-pending.json.
2. scene.rename from the agent then edit.undo: no undo before -> name restored after.
3. Non-UI scene.delete, a replacing project.open and an overwriting project.save: run or unreachable before -> CONFIRMATION_REQUIRED after; the UI path still runs.
4. inspect_studio document lists the scenes and project name matching the saved .cclayproject projection: missing before -> equal after.
5. A direct setScenes outside a run in dev: allowed before -> throws after.
6. Metric: (b) about +38 sites.
7. npm run build exits 0, the existing suites pass unchanged, and the browser smoke tests pass.

PR rules

One PR on feat/issue-461 with (#461) in the title, against main. Attach the red/green commit list and the test output. Do not merge.