Fix Shift+F1 settings, PR diff file list, and F3 on ".."

[bluestreak01]

Summary

• PR diff stale files: Fetch origin/{base_branch} before git diff --name-status so the merge base is current and the changed file list matches GitHub
• Shift+F1 (Settings) unreachable from bottom panels: The ToggleSettings action was swallowed by panel-specific handlers in handle_action (Diff, CI, Claude, Shell). Fixed by dispatching ToggleSettings before the bottom-panel block. Also moved the settings dialog key mapping above the bottom-panel key block so Esc/arrows work when settings is opened from a bottom panel. Added Shift+F1 to hex editor and diff viewer key handlers.
• F3 on ".." computed parent size: handle_calc_size now scans current_dir when ".." is selected, using entry.path as the dir_sizes key so the result displays in the size column. Added start_size_calc_at(key, scan_path) to decouple the lookup key from the scan target.

Test plan

• Open a PR branch, press Ctrl+D — verify file list matches gh pr diff --name-only
• Press Shift+F1 from file panel, Ctrl+D panel, shell, CI panel, hex editor, diff viewer — settings dialog should open from all
• While settings is open, verify Esc closes it and arrow keys navigate
• Navigate to a directory, press F3 on ".." — verify current directory size appears in the size column

🤖 Generated with Claude Code