fix(mcp): expose edit_note operation enum

[phernandez]

Why

• OpenAI's app submission review flagged edit_note.operation as a free-form string even though Basic Memory only supports a fixed set of edit operations.
• Exposing the supported operations in the MCP tool schema lowers incorrect-call risk without changing runtime behavior.

What Changed

• Added a single EDIT_OPERATIONS source of truth in src/basic_memory/mcp/tools/edit_note.py.
• Annotated the edit_note.operation parameter with JSON schema enum metadata while keeping the existing string runtime validation.
• Added a tool-contract regression that asserts the protocol-level edit_note.operation schema advertises the supported enum values.

Implementation Details

• Kept the Python parameter type as str instead of a Literal so direct Python callers, CLI paths, and invalid-operation tests do not need casts.
• The enum is emitted through Field(json_schema_extra={"enum": ...}), which FastMCP includes in tools/list while preserving the existing docstring-derived description.
• Runtime validation still rejects unsupported operations before the edit request is sent.

Testing

Automated

• uv run pytest tests/mcp/test_tool_contracts.py -q: passed, 4 passed.
• just fast-check: passed; cold testmon selected a broad run, 3397 passed, 43 skipped, 20 warnings.
• uv run ruff check src/basic_memory/mcp/tools/edit_note.py tests/mcp/test_tool_contracts.py: passed.
• uv run ruff format --check src/basic_memory/mcp/tools/edit_note.py tests/mcp/test_tool_contracts.py: passed.
• uv run ty check src tests test-int: passed.

Manual

• Inspected mcp.list_tools() for edit_note and confirmed inputSchema.properties.operation.enum contains append, prepend, find_replace, replace_section, insert_before_section, and insert_after_section.

Risks / Follow-ups

• Low risk: this changes schema metadata and reuses the existing validation path.
• Follow-up: once merged, Basic Memory Cloud should bump its basic-memory dependency so the hosted MCP endpoint advertises the new schema.