feat(xref): move term autocomplete from client to server

[marcoscaceres]

Summary

• Adds GET /xref/meta/terms/search?q=<query>&limit=<n> endpoint
• Binary search for prefix matches + linear scan infix fallback on a pre-sorted 22K terms array
• Case-insensitive matching, original-case results, 24h cache
• Client drops the 483KB terms download; autocomplete uses 150ms-debounced server fetch instead
• Existing /xref/meta/terms endpoint unchanged (backward compatible)
• 12 unit tests for the search logic

Closes #226

Test plan

• pnpm run build passes
• pnpm test passes (82 specs)
• curl 'localhost:8000/xref/meta/terms/search?q=event&limit=5' returns JSON array
• Load /xref in browser, verify autocomplete works with debounced server fetch
• Verify initial page load no longer includes terms in the meta payload
• GET /xref/meta/terms still returns the full array (backward compat)

[Copilot]

Pull request overview

This PR moves xref term autocomplete from the browser to the server by adding a dedicated term-search endpoint and updating the xref page to query it on demand instead of downloading the full term list up front. That fits the xref codebase’s existing split between server-side route handlers and a thin browser UI, and targets the payload-size problem described in #226.

Changes:

• Add a new GET /xref/meta/terms/search endpoint with cached, case-insensitive term lookup over a prebuilt index.
• Update the xref client to stop requesting the full terms payload and instead fetch debounced autocomplete suggestions from the new endpoint.
• Add route-level tests for the new term-search behavior; also align one baseline background worker type import with the existing worker-queue pattern.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/routes/xref/terms.test.js	Adds unit tests covering new server-side xref term search behavior.
static/xref/script.js	Switches autocomplete from client-side Fuse search to debounced server fetches and trims initial metadata fetch.
routes/xref/terms.get.ts	Introduces the new xref term search endpoint and in-memory sorted term index.
routes/xref/index.ts	Wires the new /meta/terms/search route into the xref router.
routes/api/baseline/update.ts	Updates the worker module type import to match the existing typed background-task-queue pattern.

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