Overhaul command palette UX

Six-phase sweep: section headers (Focused / Open / Spawn / Quit) with
header-skip cursor; chip strip mirroring sw/sp/k macros, driven by
Tab; unified Spawn verbs across agent / process / terminal / custom;
dropped duplicate global Close list in favor of Ctrl-X inline close
on a Switch row plus the [Close] chip; scored matching (prefix >
word-boundary > substring > fuzzy) with matched-char highlighting;
title bar surfaces focus subject; rename forms split long subject
onto its own row; new Alt-1..9 quick-pick, Home/End, ? help overlay,
and Ctrl-R relaunch toggle inside the spawn-process form. Scroll
indicator and cursor/total counter round out the footer.

internal/harness/scenarios/rename_process_via_palette.json

@@ -16,7 +16,7 @@
     { "type": "send_chord", "chord": "ctrl-k" },
     { "type": "send_text", "text": "Rename process" },
     { "type": "send_chord", "chord": "enter" },
-    { "type": "wait_text", "contains": "Rename process", "timeout_ms": 3000 },
+    { "type": "wait_text", "contains": "process: original", "timeout_ms": 3000 },
     { "type": "send_chord", "chord": "ctrl-u" },
     { "type": "send_text", "text": "renamed-pane" },
     { "type": "send_chord", "chord": "enter" },