feat(shell): enhance log browser, add yay wrapper, and integrate starship OSC prompt markers

- logs.fish: add yay category, ov-powered viewing for paru/yay (section
  headers, color highlights, ==> AUR build markers) and scrollback logs
  (OSC 133;A sticky prompt headers); add fzf Ctrl-D delete with Y/n
  confirm and list refresh, ? toggleable help overlay; run
  _scrollback_prune_junk before building file list
- _scrollback_prune_junk: new utility to remove empty, single-line, and
  Kitty tab-rename noise logs before display and before max-file pruning;
  called from both logs and smart_exit
- smart_exit: call _scrollback_prune_junk before counting toward max files
- conf.d/yay-wrapper.fish: auto-generate ~/.local/bin/yay logging wrapper
  mirroring paru-wrapper; tees output to timestamped logs, prunes old ones
- conf.d/starship.fish: move fish_prompt from config.fish; emit OSC 133;A
  after the prompt's leading newline so the marker lands on the info-bar
  line rather than the blank line above it; guard with type -q starship so
  clean fish sessions use built-in markers unchanged
- config.fish: remove inline fish_prompt block (now in conf.d/starship.fish);
  add return sentinel at EOF to prevent tool-injected init lines from running
- completions/ov.fish: add ov tab completions
- README.md: document all of the above

functions/smart_exit.fish

@@ -50,7 +50,10 @@ function smart_exit --description 'Capture colorized scrollback before exiting,
             end
         end
 
-        # 4. Automatic Pruning Logic
+        # 4. Prune junk logs before counting toward the max
+        _scrollback_prune_junk $snapshot_dir
+
+        # 5. Automatic Pruning Logic
         set -l current_logs $snapshot_dir/scrollback_*.log
         if test -f "$current_logs[1]"
             set -l total_files (count $current_logs)