fix: Expose an MCP tool for incremental index refresh

[linze0721]

Summary

Adds a first-class MCP tool sync_index so clients can incrementally refresh existing indexes via Context.reindexByChange, without force=true full reindex or out-of-band ~/.context/.sync-trigger touches.

Changes

Area	What changed
packages/mcp/src/sync.ts	New syncIndex({ path?, wait? }) and runSyncLocked; handleSyncIndex delegates to shared lock + per-codebase reindexByChange using snapshot-stored splitter/ignore/custom extensions. Returns stats { added, modified, removed } and clear outcomes when lock busy (wait: false) or path not indexed.
packages/mcp/src/handlers.ts	handleSyncIndex validates optional absolute path against indexed snapshot, invokes SyncManager.syncIndex, returns JSON tool result.
packages/mcp/src/index.ts	Registers sync_index in ListTools + CallTool dispatch (optional path, wait default true).
packages/mcp/src/sync-index.test.ts	Unit tests for tool wiring, path validation, wait/lock behavior, stats shape (10 tests in MCP package suite).
packages/mcp/README.md, CONTRIBUTING.md	Document sync_index parameters and behavior; clarify CLAUDE_CONTEXT_TRIGGER_WATCHER watches only ~/.context/.sync-trigger, not project directories.

Verification

pnpm --filter @zilliz/claude-context-core build && pnpm --filter @zilliz/claude-context-mcp test

All tests passed.

Git

• Branch: berserk/7368c510-3d76-41e5-ae16-462eae4765ad
• Commit: 6b055ca
• Pushed to origin

Addresses zilliztech/claude-context#394 (related #238).

Commit

6b055ca

Branch

berserk/7368c510-3d76-41e5-ae16-462eae4765ad

Fixes #394