Add optional blake3 hashing during asset scanning

- Make blake3 import lazy in hashing.py (only imported when needed)
- Add compute_hashes parameter to AssetSeeder.start(), build_asset_specs(), and seed_assets()
- Fix missing tag clearing: include is_missing states in sync when update_missing_tags=True
- Clear is_missing flag on cache states when files are restored with matching mtime/size
- Fix validation error serialization in routes.py (use json.loads(ve.json()))

Amp-Thread-ID: https://ampcode.com/threads/T-019c3614-56d4-74a8-a717-19922d6dbbee
Co-authored-by: Amp <amp@ampcode.com>

app/assets/database/queries/asset.py

@@ -85,6 +85,6 @@ def bulk_insert_assets(
     """Bulk insert Asset rows. Each dict should have: id, hash, size_bytes, mime_type, created_at."""
     if not rows:
         return
-    ins = sqlite.insert(Asset)
+    ins = sqlite.insert(Asset).on_conflict_do_nothing(index_elements=[Asset.hash])
     for chunk in iter_chunks(rows, calculate_rows_per_statement(5)):
         session.execute(ins, chunk)

app/assets/database/queries/common.py

@@ -23,8 +23,8 @@ def iter_chunks(seq, n: int):
 def iter_row_chunks(rows: list[dict], cols_per_row: int) -> Iterable[list[dict]]:
     """Yield chunks of rows sized to fit within bind param limits."""
     if not rows:
-        return []
-    rows_per_stmt = max(1, MAX_BIND_PARAMS // max(1, cols_per_row))
+        return
+    rows_per_stmt = calculate_rows_per_statement(cols_per_row)
     for i in range(0, len(rows), rows_per_stmt):
         yield rows[i : i + rows_per_stmt]