docs(diff-ux): add ASCII wireframes for every Part I surface and state

Nine frames grounded in the real chrome captured during the tmux
exploration: the Review Session container in stack and split layouts
(worktree door), the Review Branch door in flattened and per-commit
lenses, the History door with its shared-renderer detail pane, the agent
door with baseline picker and related-changes nudge dialogs, the Review…
picker palette, and the buffer lens with a hunk expanded in place.

Each frame annotates what it encodes (enclosing-context hunk headers,
copy-safe bodies, session-wide counters, viewed/kept progress, comment
severity badges, lens-stable comments) so the wireframes double as the
spec for the chrome contract.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01756Rh35n65zC4xHQcQAqBL

Author: claude