Move blake3 hash resolution to asset_management service

Extract resolve_hash_to_path() into asset_management.py and remove
_resolve_blake3_to_path from server.py. Also revert loopback origin
check to original logic.

Amp-Thread-ID: https://ampcode.com/threads/T-019ce023-3384-7560-bacf-de40b0de0dd2
Co-authored-by: Amp <amp@ampcode.com>

app/assets/services/asset_management.py

@@ -280,6 +280,39 @@ def list_assets_page(
         return ListAssetsResult(items=items, total=total)
 
 
+def resolve_hash_to_path(
+    asset_hash: str,
+) -> DownloadResolutionResult | None:
+    """Resolve a blake3 hash to an on-disk file path.
+
+    Returns a DownloadResolutionResult with abs_path, content_type, and
+    download_name, or None if no asset or live path is found.
+    """
+    with create_session() as session:
+        asset = queries_get_asset_by_hash(session, asset_hash)
+        if not asset:
+            return None
+        refs = list_references_by_asset_id(session, asset_id=asset.id)
+        abs_path = select_best_live_path(refs)
+        if not abs_path:
+            return None
+        display_name = os.path.basename(abs_path)
+        for ref in refs:
+            if ref.file_path == abs_path and ref.name:
+                display_name = ref.name
+                break
+        ctype = (
+            asset.mime_type
+            or mimetypes.guess_type(display_name)[0]
+            or "application/octet-stream"
+        )
+    return DownloadResolutionResult(
+        abs_path=abs_path,
+        content_type=ctype,
+        download_name=display_name,
+    )
+
+
 def resolve_asset_for_download(
     reference_id: str,
     owner_id: str = "",