feat(mcp): add access-tier registry

[solomonneas]

What changed

• declare read, safe-write, or destructive access tiers for all 74 Immich MCP tools
• derive MCP readOnlyHint and destructiveHint annotations from those tiers
• reject registered/declared tool drift before the server connects its transport
• test the registry against executor gates parsed from every tool handler

Why

This is Step 2 of the dynamic-tool loading runbook, following the frozen benchmark in #10. The tier map repeats safety facts already enforced by executor gates, so the test derives each tool's maximum tier independently from requireWrites, requireConfirm, inline confirmation guards, and local helper calls.

immich_restore_by_query is classified as destructive because its no-filter path requires confirm: true, even though that check is inline rather than delegated to requireConfirm.

Verification

• npm test - 25 files and 249 tests passed
• npm run typecheck - passed
• npm run build - passed