Add distribution-owned response feedback UI

[comp615]

This PR description was generated by AMP.

Summary

Berd distributions need a generic way to collect turn-level response ratings without putting a company-specific telemetry endpoint or schema in the public app.

This adds opt-in thumbs-up/down controls tied to the canonical assistant response, session ID, and message ID. Stock Berd uses a typed no-op transport seam; distributions can supply their own sink and enable the UI through runtime config. Mounting, hovering, focusing, or revealing controls emits nothing; only explicit good, bad, and cleared transitions are sequenced, so the highest sequence is the final state.

Related issue

N/A — no duplicate issue or PR found.

Testing

bin/just check
bin/pnpm vitest run src/features/chat/response-feedback src/shared/runtime-config/schema.test.ts
bin/just _tauri-cargo-unix check --features block-feedback

AI tool validation prompt

Copy and paste into your AI tool:

Review block/berd branch ccroom/response-feedback-ui and verify:
1. Run the focused response-feedback and runtime-config tests.
2. Confirm stock Berd sends no feedback events, while the typed sink receives session ID, message ID, appearance ID, sequence, and response only when the user changes a rating, and that the highest sequence yields the final state.
3. Confirm only the canonical terminal assistant response receives controls in classic and virtual transcripts.