Fix registry lookups to use cid, remove dead legacy code

- Fix all registry lookups to use "cid" instead of "hash" key
  - app/routers/recipes.py: asset and effect resolution
  - tasks/execute_sexp.py: effect config lookups
  - server_legacy.py references (now deleted)
- Prefer IPFS CID over local hash in cache operations
  - cache_service.py: import_from_ipfs, upload_content
  - orchestrate.py: plan caching
  - legacy_tasks.py: node hash tracking

Remove ~7800 lines of dead code:
- server_legacy.py: replaced by modular app/ structure
- tasks/*_cid.py: unused refactoring only imported by server_legacy

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/services/cache_service.py

@@ -432,8 +432,8 @@ class CacheService:
                 return None, f"Could not fetch CID {ipfs_cid} from IPFS"
 
             # Store in cache
-            cached, _ = self.cache.put(tmp_path, node_type="import", move=True)
-            cid = cached.cid
+            cached, ipfs_cid = self.cache.put(tmp_path, node_type="import", move=True)
+            cid = ipfs_cid or cached.cid  # Prefer IPFS CID
 
             # Save to database
             await self.db.create_cache_item(cid, ipfs_cid)
@@ -468,7 +468,7 @@ class CacheService:
 
             # Store in cache (also stores in IPFS)
             cached, ipfs_cid = self.cache.put(tmp_path, node_type="upload", move=True)
-            cid = cached.cid
+            cid = ipfs_cid or cached.cid  # Prefer IPFS CID
 
             # Save to database with detected MIME type
             await self.db.create_cache_item(cid, ipfs_cid)