Refactor tests for execution plan and add comprehensive storage tests

- Updated `TestModuleSingletons` in `test_execution_plan.py` to reflect new agent templates and playbook names.
- Changed assertions in playbook tests to match updated templates and agents.
- Introduced `test_storage.py` to cover the storage layer, including encryption, BlobStore, and VectorStore functionalities.
- Added tests for S3 interactions, ensuring upload, download, delete, and list operations work as expected.
- Implemented mock tests for Pinecone and Qdrant vector stores to validate upsert, search, and delete operations.

app/storage/encryption.py

@@ -0,0 +1,32 @@
+"""Integrity verification only — the backend NEVER decrypts user data."""
+
+from __future__ import annotations
+
+import hashlib
+import hmac
+
+from fastapi import HTTPException
+
+
+def verify_checksum(blob: bytes, checksum: str) -> bool:
+    """Return ``True`` if SHA-256(blob) matches *checksum*.
+
+    Uses ``hmac.compare_digest`` for constant-time comparison to prevent
+    timing-based side-channel attacks.
+    """
+    computed = hashlib.sha256(blob).hexdigest()
+    return hmac.compare_digest(computed, checksum)
+
+
+def reject_if_tampered(blob: bytes, checksum: str) -> None:
+    """Raise ``HTTP 400`` if the blob does not match its checksum.
+
+    Call this before storing or forwarding any client-provided blob.
+    The backend never holds decryption keys — this check only verifies
+    that the opaque bytes arrived intact.
+    """
+    if not verify_checksum(blob, checksum):
+        raise HTTPException(
+            status_code=400,
+            detail="Checksum mismatch: blob integrity check failed",
+        )