Add IPFS CID support for asset lookup

- Upload endpoint returns both CID and content_hash
- Cache manager handles both SHA3-256 hashes and IPFS CIDs
- get_by_cid() fetches from IPFS if not cached locally
- Execute tasks support :cid in addition to :hash

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

app/routers/cache.py

@@ -209,9 +209,9 @@ async def upload_content(
     ctx: UserContext = Depends(require_auth),
     cache_service: CacheService = Depends(get_cache_service),
 ):
-    """Upload content to cache."""
+    """Upload content to cache and IPFS."""
     content = await file.read()
-    content_hash, error = await cache_service.upload_content(
+    content_hash, ipfs_cid, error = await cache_service.upload_content(
         content=content,
         filename=file.filename,
         actor_id=ctx.actor_id,
@@ -221,7 +221,8 @@ async def upload_content(
         raise HTTPException(400, error)
 
     return {
-        "content_hash": content_hash,
+        "cid": ipfs_cid,
+        "content_hash": content_hash,  # Legacy, for backwards compatibility
         "filename": file.filename,
         "size": len(content),
         "uploaded": True,