fix(review): persist file comment drafts across close/reopen

[codythatsme]

Summary

• File comment popovers in the code review UI dropped in-progress text whenever the popover was dismissed (click-outside / Escape / close button) — text and images lived in CommentPopover's local useState, so unmount erased them. Reopening on the same file started from a blank textarea.
• The line-comment toolbar already solves this with a module-level draft map. This PR mirrors that pattern in CommentPopover behind an opt-in draftKey prop so existing call sites that don't want draft persistence are unaffected.
• Wire both file-comment call sites — AllFilesDiffView and DiffViewer — with draftKey={file:${filePath}}. Drafts are cleared on submit.

Recording

CleanShot.2026-05-13.at.23.33.19.2.mp4

Test plan

• bun run --cwd apps/review build && bun run build:hook — clean build
• Open a file-level comment popover, type some text, click outside — reopen the same file's popover, draft is restored
• Same flow with Escape and the X close button — draft restored in both cases
• Attach an image, dismiss, reopen — image attachment is restored alongside text
• Submit the comment — reopen the same file's popover, textarea is empty (draft cleared on submit)
• Open file A's popover, type, dismiss; open file B's popover — file B is blank (drafts keyed per file, no cross-talk)
• Line-comment toolbar still behaves as before (regression check on the existing line-comment draft path)