fix(app): restore review line comments

[Hona]

Summary

• open a comment draft whenever a diff line selection completes
• wire the custom comment button through Pierre's gutter utility API
• remove the redundant line-number-specific comment completion path
• cover code clicks, gutter clicks, gutter range selection, and hover comments in Chromium

Closes #32835.

Rationale

Comment creation is a policy of the line-comment controller, so all completed selections follow one path: onLineSelectionEnd opens the draft. The file viewer remains responsible only for reporting selections. Pierre requires enableGutterUtility and renderGutterUtility for the hover action, so the internal naming now matches that API.

Verification

• exact upstream/dev: all four new Playwright cases fail
• fixed branch: all four cases pass twice without changes
• bun typecheck in packages/ui
• bun typecheck in packages/app
• pre-push full monorepo typecheck: 23/23 tasks passed
• Prettier and git diff --check

[Copilot]

Pull request overview

Restores inline review line-comment creation in the app’s diff viewer by aligning the UI integration with Pierre’s gutter-utility API, ensuring completed line selections consistently open a comment draft, and adding regression coverage for the previously broken interactions.

Changes:

• Switch diff viewers from the old hover-utility API to Pierre’s gutter-utility API (enableGutterUtility / renderGutterUtility).
• Simplify line-comment controller flow so all completed selections open drafts via onLineSelectionEnd, removing the separate line-number completion path.
• Add Playwright regression coverage (click code, click gutter, drag gutter range, hover gutter “Comment” button) and extend the e2e mock server to serve /vcs/diff.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/ui/src/components/session-review.tsx	Updates review diff viewer wiring to use gutter utility props and renderer.
packages/ui/src/components/line-comment-annotations.tsx	Refactors line-comment controller to open drafts on selection end and renames hover renderer to gutter renderer.
packages/app/src/pages/session/file-tabs.tsx	Updates the file tab diff/text viewer wiring to use gutter utility props and renderer.
packages/app/e2e/utils/mock-server.ts	Adds optional /vcs/diff response support for e2e tests.
packages/app/e2e/regression/review-line-comment.spec.ts	Adds Chromium regression tests covering restored inline comment interactions.

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[max-wittig]

Thanks for the fix here! I just wanted to make an MR to bring inline comments back