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/config.py

@@ -22,6 +22,8 @@ class Settings(BaseSettings):
     backup_dir: Path = Path("./backups")
     run_dir: Path = Path("./run")
     project_registry_path: Path = Path("./config/project-registry.json")
+    assets_dir: Path | None = None
+    assets_max_upload_bytes: int = 20 * 1024 * 1024  # 20 MB per upload
     host: str = "127.0.0.1"
     port: int = 8100
     db_busy_timeout_ms: int = 5000
@@ -76,6 +78,10 @@ class Settings(BaseSettings):
     def resolved_data_dir(self) -> Path:
         return self._resolve_path(self.data_dir)
 
+    @property
+    def resolved_assets_dir(self) -> Path:
+        return self._resolve_path(self.assets_dir or (self.resolved_data_dir / "assets"))
+
     @property
     def resolved_db_dir(self) -> Path:
         return self._resolve_path(self.db_dir or (self.resolved_data_dir / "db"))
@@ -132,6 +138,7 @@ class Settings(BaseSettings):
             self.resolved_backup_dir,
             self.resolved_run_dir,
             self.resolved_project_registry_path.parent,
+            self.resolved_assets_dir,
         ]
 
     @property