feat(mcp): warn when project indexes need rebuilding

[cbeaulieu-gt]

Summary

• warn each MCP client once per resolved project when its index predates the running extraction engine
• keep warning state isolated per client across direct, shared-daemon, and daemon-to-local-fallback execution
• always report index-build version, running version, and rebuild guidance from codegraph_status
• document the behavior in the changelog

The check is local, preserves the nonblocking initialize handshake, and never starts indexing automatically.

Verification

• npm run build
• npx vitest run __tests__/mcp-index-version-warning.test.ts __tests__/mcp-staleness-banner.test.ts __tests__/upgrade.test.ts --maxWorkers=1 --minWorkers=1 — 69 passed
• live daemon feature filter run three consecutive times — 6 passed total
• git diff upstream/main...HEAD --check
• post-commit artifact audit confirmed all eight changed files are present in HEAD
• independent code review: no findings

Known upstream baseline

The broader upstream test suite is not currently zero-failure on this Windows host. Previously reproduced failures map to existing upstream issues/PRs, including daemon teardown EPERM cleanup covered by #1717; the focused feature assertions above pass.

Closes #1852

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