feat(tui-go): slash command menu in the chat input

Typing `/` as the first char of a chat line opens the command palette inline
(opencode-style), instead of typing a literal slash; mid-line `/` stays literal.
Factors openPalette() (shared with the `p` key) and advertises `/ cmds` in the
insert-mode footer when the line is empty.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/tui-go/internal/app/update.go

@@ -229,9 +229,7 @@ func (m Model) handleNormalKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 	case "k":
 		m.navUp()
 	case "p":
-		m.overlay = OverlayPalette
-		m.paletteFilter = ""
-		m.paletteIndex = 0
+		m.openPalette()
 	case "e":
 		m.overlay = OverlayEventInspector
 		m.overlayEventIdx = 0
@@ -408,12 +406,28 @@ func (m Model) handleInsertKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 			m.historyNext()
 		}
 	case tea.KeyRunes, tea.KeySpace:
+		// opencode-style slash commands: `/` as the first char of a chat line opens the
+		// command palette inline instead of typing a literal slash. Mid-line `/` is literal.
+		if m.inputMode == ModeRouter && m.inputBuffer == "" && string(k.Runes) == "/" {
+			m.editMode = ModeNormal
+			m.clearInput()
+			m.openPalette()
+			return m, nil
+		}
 		m.appendRunes(string(k.Runes))
 		m.syncFilter()
 	}
 	return m, nil
 }
 
+// openPalette opens the command palette with a cleared filter. Shared by the `p`
+// normal-mode key and the inline `/` trigger in the chat input.
+func (m *Model) openPalette() {
+	m.overlay = OverlayPalette
+	m.paletteFilter = ""
+	m.paletteIndex = 0
+}
+
 // beginIntent stashes the chosen workflow and switches to a text-entry prompt for the
 // freeform request. Submitting sends StartSession(id, intent); an empty line starts with no
 // intent (fixed-task workflows). Esc cancels.