Remove old tfidf worker code

[mjbvz]

No description provided.

[Copilot]

Pull request overview

Removes the legacy TF‑IDF implementation and its worker wiring from the Copilot extension codebase, simplifying the build/package outputs by dropping unused search/indexing code.

Changes:

• Deleted the TF‑IDF SQLite-backed index implementation, worker entrypoint, and messaging helpers.
• Removed the TF‑IDF unit tests.
• Updated build/packaging configuration to stop producing and shipping the tfidfWorker bundle, and removed ESLint config references.

Show a summary per file

File	Description
extensions/copilot/src/platform/tfidf/node/tfidfWorker.ts	Removed the TF‑IDF worker implementation and RPC host/worker plumbing.
extensions/copilot/src/platform/tfidf/node/tfidfMessaging.ts	Removed the object rewrite helper used for worker message serialization.
extensions/copilot/src/platform/tfidf/node/tfidf.ts	Removed the SQLite-backed PersistentTfIdf implementation and search logic.
extensions/copilot/src/platform/tfidf/node/test/tfidf.spec.ts	Removed TF‑IDF-specific Vitest unit tests.
extensions/copilot/eslint.config.mjs	Removed references to the deleted TF‑IDF files from the ESLint config.
extensions/copilot/.vscodeignore	Stopped including dist/tfidfWorker.js in the packaged extension.
extensions/copilot/.esbuild.ts	Removed the TF‑IDF worker entry from the esbuild worker bundle list.

Copilot's findings

• Files reviewed: 7/7 changed files
• Comments generated: 0