Add context-aware items to the command palette

When opened with Ctrl-K, the palette now prepends entries for whatever
is currently focused:

- Focused scratchpad: Delete / Rename (inline form) / Edit (fire-and-
  forget zed launch with stdio detached so the TUI is not suspended).
- Focused agent: Rename (inline form) / Close.
- Focused process: Rename / Delete (drops the entry; SIGKILL if alive)
  / Stop (SIGTERM, keep entry) / Restart (same argv).

The rename UX is a single-field inline form that mirrors the existing
spawn-process form, so the modal-input contract is unchanged.
scratchpad.Store grows Delete / Rename / Path so the palette can act
on a pad file by name. focusedPad is plumbed onto uiState ahead of the
scratchpad-focus UI work; until that lands it stays empty and the
scratchpad-context entries simply never surface.

Tested with palette_context_test.go and a new rename_process_via_palette
harness scenario.

internal/app/palette_input_test.go

@@ -7,7 +7,7 @@ import (
 )
 
 func newTestPalette() *paletteState {
-	return newPalette(nil, "", preset.Set{})
+	return newPalette(nil, "", "", preset.Set{})
 }
 
 func TestPaletteIgnoresKittyReleaseEvent(t *testing.T) {
@@ -49,7 +49,7 @@ func TestPaletteBareEscCancels(t *testing.T) {
 
 func TestPaletteKittyArrowsNavigate(t *testing.T) {
 	pr := []*preset.Preset{{Name: "a"}, {Name: "b"}, {Name: "c"}}
-	p := newPalette(nil, "", preset.Set{Agents: pr})
+	p := newPalette(nil, "", "", preset.Set{Agents: pr})
 	if p.cursor != 0 {
 		t.Fatalf("initial cursor %d", p.cursor)
 	}
@@ -70,7 +70,7 @@ func TestPaletteKittyArrowsNavigate(t *testing.T) {
 
 func TestPaletteLegacyArrowsStillWork(t *testing.T) {
 	pr := []*preset.Preset{{Name: "a"}, {Name: "b"}}
-	p := newPalette(nil, "", preset.Set{Agents: pr})
+	p := newPalette(nil, "", "", preset.Set{Agents: pr})
 	_, _, adv := p.handleInput([]byte("\x1b[B"), 0)
 	if adv != 3 {
 		t.Fatalf("advance %d", adv)
@@ -82,7 +82,7 @@ func TestPaletteLegacyArrowsStillWork(t *testing.T) {
 
 func TestPaletteKittyEnterAccepts(t *testing.T) {
 	pr := []*preset.Preset{{Name: "x"}}
-	p := newPalette(nil, "", preset.Set{Agents: pr})
+	p := newPalette(nil, "", "", preset.Set{Agents: pr})
 	action, done, _ := p.handleInput([]byte("\x1b[13u"), 0)
 	if !done || action.kind != "spawn-agent" {
 		t.Fatalf("Enter via CSI u didn't accept: action=%+v done=%v", action, done)
@@ -112,7 +112,7 @@ func TestPaletteLegacyPrintableTypes(t *testing.T) {
 // non-empty command line emits the submit action with relaunch reflecting
 // the checkbox state.
 func TestPaletteSpawnProcessFormFlow(t *testing.T) {
-	p := newPalette(nil, "", preset.Set{})
+	p := newPalette(nil, "", "", preset.Set{})
 	// The "Spawn process…" entry is the only non-Quit item with an
 	// empty preset list. Locate its index by scanning items.
 	idx := -1
@@ -165,7 +165,7 @@ func TestPaletteSpawnProcessFormFlow(t *testing.T) {
 }
 
 func TestPaletteSpawnProcessFormEmptyCommandCancels(t *testing.T) {
-	p := newPalette(nil, "", preset.Set{})
+	p := newPalette(nil, "", "", preset.Set{})
 	p.mode = paletteModeSpawnForm
 	p.form = &spawnProcessForm{}
 	action, done, _ := p.handleInput([]byte("\r"), 0)
@@ -175,7 +175,7 @@ func TestPaletteSpawnProcessFormEmptyCommandCancels(t *testing.T) {
 }
 
 func TestPaletteSpawnProcessFormEscCancels(t *testing.T) {
-	p := newPalette(nil, "", preset.Set{})
+	p := newPalette(nil, "", "", preset.Set{})
 	p.mode = paletteModeSpawnForm
 	p.form = &spawnProcessForm{cmd: []rune("x")}
 	action, done, _ := p.handleInput([]byte{0x1b}, 0)