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/phase8/p6-casa-sol-save.md

@@ -0,0 +1,77 @@
+# Phase 8 P6 — Casa del Sol via save_scene
+
+Generated: 2026-04-19T18:20:19.643Z
+Transport: stdio (spawned `bun /Users/adrian/Desktop/editor/.worktrees/mcp-server/packages/mcp/dist/bin/pascal-mcp.js --stdio`)
+PASCAL_DATA_DIR: `/tmp/pascal-phase8`
+Editor URL: http://localhost:3002
+
+## Result summary
+
+- Steps passed: **13/13**
+- Initial node count: 3
+- Final node count: **39** (threshold ≥ 30)
+- doors=6, windows=6, zones=9, walls=9, fences=5, slabs=1
+- All validate_scene calls valid=true: **true**
+- Saved scene id: `6f87c59c1535`
+- Scene file: `/tmp/pascal-phase8/scenes/6f87c59c1535.json`
+
+### Open in browser: http://localhost:3002/scene/6f87c59c1535
+
+## Per-step results
+
+| # | Step | Status | Duration | Summary |
+|---|------|--------|----------|---------|
+| 1 | discover | PASS | 2ms | building=building_16mw8oy88f952is9, level=level_3jbpcuma0wfwclex |
+| 2 | perimeter walls | PASS | 2ms | 4 walls |
+| 3 | interior walls | PASS | 0ms | 5 walls |
+| 4 | zones | PASS | 2ms | 7 zones |
+| 5 | openings | PASS | 3ms | 6 doors, 6 windows, 0 failures |
+| 6 | pool zone + slab | PASS | 1ms | zone=zone_lnki9rxnoyq72rwi, slab=slab_rfyzzvcxlkbgif1w |
+| 7 | privacy fences | PASS | 1ms | 5 fences |
+| 8 | garden zone | PASS | 0ms | zone=zone_6l4ls8mr4rtfvsye |
+| 9 | save_scene | PASS | 6ms | id=6f87c59c1535, nodeCount=39, size=29677B, url=/scene/6f87c59c1535 |
+| 10 | file on disk | PASS | 0ms | /tmp/pascal-phase8/scenes/6f87c59c1535.json (29677B) |
+| 11 | GET /api/scenes/:id | PASS | 9ms | 200 OK, 39 nodes |
+| 12 | GET /scene/:id (HTML) | PASS | 237ms | 200 OK, text/html; charset=utf-8, 72918B |
+| 13 | write v2 scene.json | PASS | 1ms | 26761B -> /Users/adrian/Desktop/editor/.worktrees/mcp-server/packages/mcp/test-reports/phase8/casa-sol-v2.json |
+
+## Validation history
+
+| Phase | valid | errors |
+|-------|-------|--------|
+| initial | true | 0 |
+| afterWalls | true | 0 |
+| afterZones | true | 0 |
+| afterOpenings | true | 0 |
+| afterPool | true | 0 |
+| afterFences | true | 0 |
+| afterGarden | true | 0 |
+| final | true | 0 |
+
+## save_scene response
+
+```json
+{
+  "id": "6f87c59c1535",
+  "name": "Casa del Sol",
+  "projectId": null,
+  "thumbnailUrl": null,
+  "version": 1,
+  "createdAt": "2026-04-19T18:20:19.389Z",
+  "updatedAt": "2026-04-19T18:20:19.389Z",
+  "ownerId": null,
+  "sizeBytes": 29677,
+  "nodeCount": 39,
+  "url": "/scene/6f87c59c1535"
+}
+```
+
+## Assertions
+
+- [x] ≥30 nodes total
+- [x] validate_scene valid:true at every phase
+- [x] save_scene returned id=`6f87c59c1535`
+- [x] file exists on disk at `/tmp/pascal-phase8/scenes/6f87c59c1535.json`
+- [x] GET /api/scenes/<id> returned 200 with matching node count
+- [x] GET /scene/<id> returned 200 HTML
+- [x] wrote `/Users/adrian/Desktop/editor/.worktrees/mcp-server/packages/mcp/test-reports/phase8/casa-sol-v2.json`