Fixes #2300.

Before

• Review state was selected only by the current PR head SHA.
• If a reviewer completed changes_requested on sha-old and the worker pushed sha-new, the planner found no run for sha-new.
• The Reviews tab row became needs_review, but had no latestRun attached for display.
• The visible row verdict and top badge could fall back to Not run, even though the latest actual review verdict was changes_requested or approved.
• The Run review button was available, which was correct.

After

• The planner still marks the PR as needs_review when the head SHA changes, so the button stays available.
• It also attaches the newest review run for that PR as latestRun, even if that run was for a previous SHA.
• The Reviews tab now prefers latestRun.verdict when choosing the visible label.
• After changes_requested on sha-old and a push to sha-new, the row and top badge still show Changes requested.
• The user can still click Run review to send the next review request for sha-new.

Reviewer trigger behavior

• No auto-triggering is added.
• Existing trigger flow already sends a message to a live reviewer terminal via Notify/SendMessage.
• If the reviewer pane is not alive, it spawns a new reviewer with the review prompt in the launch command.

Tests

• npm run lint
• npm run frontend:typecheck
• cd backend && go test ./internal/review ./internal/httpd/...