feat(assets): binary asset store + artifact entity + wiki evidence (Issue F)

Wires visual evidence into the knowledge graph. Images, PDFs, and CAD
exports can now be uploaded, deduped by SHA-256, thumbnailed, linked to
entities via EVIDENCED_BY, and rendered inline on wiki pages. Unblocks
AKC uploading voice-session screenshots alongside extracted entities.

- assets/ module: store_asset (hash dedup + MIME allowlist + 20 MB cap),
  get_asset_binary, get_thumbnail (Pillow, on-disk cache under
  .thumbnails/<size>/), list_orphan_assets, invalidate_asset
- models/database.py: new `assets` table + indexes
- engineering/service.py: `artifact` added to ENTITY_TYPES
- api/routes.py: POST /assets (multipart), GET /assets/{id},
  /assets/{id}/thumbnail, /assets/{id}/meta, /admin/assets/orphans,
  DELETE /assets/{id} (409 if still referenced),
  GET /entities/{id}/evidence (EVIDENCED_BY artifacts with asset meta)
- main.py: all new paths aliased under /v1
- engineering/wiki.py: entity pages render EVIDENCED_BY → artifact as a
  "Visual evidence" thumbnail strip; artifact pages render the full
  image + caption + capture_context
- deploy/dalidou/docker-compose.yml: bind-mount ${ATOCORE_ASSETS_DIR}
- config.py: assets_dir + assets_max_upload_bytes settings
- requirements.txt + pyproject.toml: python-multipart, Pillow>=10.0.0
- tests/test_assets.py: 16 tests (dedup, cap, thumbnail cache, orphan
  detection, invalidate gating, API upload/fetch, evidence, v1 aliases,
  wiki rendering)
- DEV-LEDGER.md: session log + cleanup note + test_count 478 -> 494

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

src/atocore/main.py

@@ -88,6 +88,12 @@ _V1_PUBLIC_PATHS = {
     "/health",
     "/sources",
     "/stats",
+    # Issue F: asset store + evidence query
+    "/assets",
+    "/assets/{asset_id}",
+    "/assets/{asset_id}/thumbnail",
+    "/assets/{asset_id}/meta",
+    "/entities/{entity_id}/evidence",
 }
 
 _v1_router = APIRouter(prefix="/v1", tags=["v1"])