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/app/palette_context_test.go

@@ -31,8 +31,10 @@ func findItem(p *paletteState, want string) (int, *paletteItem) {
 
 func TestContextItemsScratchpad(t *testing.T) {
 	p := newPalette(nil, "", "notes.md", preset.Set{})
-	if i, _ := findItem(p, "pad-delete"); i != 0 {
-		t.Fatalf("pad-delete at %d; want top", i)
+	// pad-delete is the first selectable row; the Focused section header
+	// (a non-selectable row) sits above it.
+	if i, _ := findItem(p, "pad-delete"); i != 1 {
+		t.Fatalf("pad-delete at %d; want 1 (after Focused header)", i)
 	}
 	if _, it := findItem(p, "pad-rename-form"); it == nil || it.action.padName != "notes.md" {
 		t.Fatalf("pad-rename-form missing or wrong padName: %+v", it)