feat(mcp): add directory listing sorting

[phernandez]

Why

The hosted MCP project and folder browser needs one exact-depth directory read that includes both child folders and notes while supporting title and updated-time sorting.

Core previously exposed only its legacy filename ordering, forcing Cloud to use a notes-only fallback for non-default sorts and lose folder cards. This closes #1267 and unblocks the one-read navigation work in basic-memory-cloud#1764.

What Changed

• Added the closed title_asc, title_desc, updated_asc, and updated_desc sort contract to the directory API and typed MCP client.
• Applied deterministic, folders-first ordering before pagination.
• Exposed sorting through the public list_directory MCP tool without re-sorting the API response.
• Included the selected sort mode in semantic read-cache keys.
• Added service, API, client, MCP contract/tool, pagination, and Redis cache regression coverage.

Implementation Details

• Omitting sort preserves the existing filename-based ordering for compatibility.
• Explicit title sorts use note titles, with directory path and external ID as deterministic tie-breakers.
• Explicit updated sorts use the same identity tie-breakers before applying the timestamp as the stable primary key.
• Implicit directory entries do not have canonical update timestamps, so updated-time modes keep directories name-ascending while still placing them before files.
• Missing file timestamps fail fast instead of silently producing an unstable order.

Testing

Automated

• uv run pytest tests/services/test_directory_service.py tests/api/v2/test_directory_router.py tests/mcp/clients/test_clients.py tests/mcp/test_tool_contracts.py tests/mcp/test_tool_list_directory.py -q: 88 passed
• uv run pytest tests/services/test_directory_service.py tests/mcp/test_tool_list_directory.py -q: 47 passed
• uv run pytest tests/mcp/test_tool_contracts.py -q: 5 passed
• uv run pytest test-int/read_cache/test_api_read_cache.py::test_directory_reads_cache_then_project_invalidation_refreshes -q: 1 passed
• just fast-check: passed
• just typecheck: passed
• just doctor: passed
• just test-smoke: 1 passed

Manual

• Inspected the generated MCP input schema and confirmed the nullable sort field advertises exactly the four supported enum values.
• Verified the staged diff contained only the 11 implementation and regression-test files.

Risks / Follow-ups

• No schema migration or default behavior change.
• Cloud can remove its notes-only sorting fallback after consuming this Core contract.