fix: regenerate uv.lock files and update mcp to 1.26.0 for semantic-kernel compatibility

- Update mcp 1.23.0 → 1.26.0 in src/backend/pyproject.toml (required by semantic-kernel 1.39.4)
- Regenerate src/backend/uv.lock with updated semantic-kernel, python-multipart, and mcp versions
- Regenerate src/mcp_server/uv.lock with updated python-multipart version

Co-authored-by: Roopan-Microsoft <168007406+Roopan-Microsoft@users.noreply.github.com>

Author: Copilot

src/backend/pyproject.toml

@@ -31,7 +31,7 @@ dependencies = [
     "uvicorn==0.35.0",
     "pylint-pydantic==0.3.5",
     "pexpect==4.9.0",
-    "mcp==1.23.0",
+    "mcp==1.26.0",
     "werkzeug==3.1.5",
     "azure-core==1.38.0",
     "agent-framework>=1.0.0b251105",