fix(mcp,editor): close URL-validation bypasses surfaced by Phase 8 P4

Phase 8 parallel validation flagged two boundaries where malicious URLs
(javascript:, file:, external http:, data:text/html, ...) could be
persisted despite the AssetUrl allowlist added in Phase 7 A7:

1. `save_scene({ includeCurrentScene: false, graph })` — the graph arg
   was treated as opaque (`z.record(z.string(), z.unknown())`) and
   written to the store without re-running AnyNode.safeParse.

2. `POST /api/scenes { graph }` in the editor API — same issue; the
   Zod `graphSchema` accepted anything object-shaped.

Fixes:
- `save-scene.ts`: when `includeCurrentScene === false`, iterate every
  node and run `AnyNode.safeParse`; collect issues and throw
  `McpError(InvalidParams, 'graph_invalid', { errors })` on any
  failure.
- `app/api/scenes/route.ts`: replace `graphSchema` with a structured
  `z.object({ nodes, rootNodeIds, collections? })` + `superRefine`
  that runs `AnyNode.safeParse` on every node. Invalid → 400 with
  detailed issue paths.

Tests:
- Added `save_scene` regression test for the P4 attack
  (item.asset.src = 'javascript:alert(1)') — expected error.
- Fixed the existing `includeCurrentScene=false` test to use a
  schema-compliant site node id (the prior `id: 'root'` now fails
  the AnyNode parse, which is the desired strict behaviour).
- Full suite: 294 pass / 0 fail.

Also adds Phase 8 test-reports/phase8/** (10 agents, ~15 scripts +
markdown reports) documenting the validation run, plus minor biome
cleanups to the Phase 5/7 test artefacts (removed stale
`// biome-ignore` suppression comments that now resolve to the
already-off `noConsole` rule).

Phase 8 result summary (10 parallel agents, stdio MCP transport with
isolated data dirs):
- P1 templates: 18/18 PASS
- P2 variants: 6/7 mutations + determinism + save + combined + error
- P3 locking: 12/12 PASS (MCP + editor HTTP If-Match)
- P4 URL hardening: fixed 2 bypasses (see above)
- P5 photo-to-scene: 6/6 PASS
- P6 Casa del Sol via save_scene: 13/13 PASS
- P7 editor HTTP API: 18/18 PASS
- P8 concurrency: 4/5 PASS, flagged 2 real filesystem-store races
  (expectedVersion CAS gap + .index.json drift under parallel writes)
- P9 edge cases: 13/13 PASS (size cap, slug safety, bad inputs)
- P10 full sweep: 37/37 PASS (30 tools + 4 resources + 3 prompts)

Known follow-ups:
- FilesystemSceneStore needs a proper lockfile / atomic CAS to fix
  the P8 concurrency bugs (low priority: single-writer MCP is the
  typical case).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/mcp/test-reports/t3-scenario/run.ts

@@ -37,7 +37,6 @@ type StepResult = {
 const steps: StepResult[] = []
 
 function log(msg: string): void {
-  // biome-ignore lint/suspicious/noConsole: test script
   console.log(`[t3] ${msg}`)
 }
 
@@ -625,7 +624,6 @@ async function main(): Promise<void> {
 }
 
 main().catch((err) => {
-  // biome-ignore lint/suspicious/noConsole: test script
   console.error(err)
   process.exit(1)
 })