feat(tui-go): idle launcher — centered input + status/keys rail (Phase 1)

Replace the idle two-panel layout (session list + welcome, where the welcome
panel duplicated the list) with an opencode-style launcher: a compact, centered
input whose lower-right shows the launch target and model (chat by default), a
hideable right rail of status + quick keys, and no session list — it's a keypress
away via R.

- Tab (or w) cycles the launch target: chat → workflows → chat (launcherWf),
  shown at the input. Enter on chat starts a chat; on a workflow, StartSession
  with the typed text as the brief.
- Right rail (connection, session/active counts, i/Tab/R/?/p keys) hides via the
  new "rail" palette command. Drops automatically on narrow terminals.
- View() suppresses the bottom input bar on idle (the input is the launcher);
  footer + ? help updated to the launcher keys (help-coverage test extended).

The old idle-panel renderers (sessionRows/welcomeRows/workflowRows) are now
unused but kept in the tree pending Phase 2 + a decision on where the session
dates should live now that the idle list is gone. Multi-line input (Ctrl+J /
Alt+Enter newline) is Phase 2.

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

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

@@ -206,6 +206,12 @@ func (m Model) handleKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 			return m, nil
 		}
 	}
+	// On the idle launcher, Tab cycles the launch target (chat → workflows → chat) in any
+	// edit mode, so it works whether or not the input is focused.
+	if m.displayState() == StateIdle && k.Type == tea.KeyTab {
+		m.cycleLauncherWf()
+		return m, nil
+	}
 	if m.editMode == ModeInsert {
 		return m.handleInsertKey(k)
 	}
@@ -300,13 +306,9 @@ func (m Model) handleNormalKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 	case "m":
 		m.openModelsOverlay()
 	case "w":
+		// Launcher: w is an alias for Tab — cycle the launch target (chat / workflow…).
 		if ds == StateIdle {
-			m.wfVisible = !m.wfVisible
-			if m.wfVisible {
-				m.wfIndex = 0
-			} else {
-				m.wfIndex = -1
-			}
+			m.cycleLauncherWf()
 		}
 	case "l":
 		if ds != StateIdle {
@@ -1074,6 +1076,7 @@ func paletteCommands() []paletteCmd {
 		{"config", "g", "edit config", "view / change correx settings"},
 		{"grants", "G", "grants", "view / revoke standing grants"},
 		{"statusbar", "", "status bar", "show / hide status-bar segments"},
+		{"rail", "", "idle rail", "show / hide the idle status + keys rail"},
 		{"actions", "", "inline actions", "show / hide tool & action rows in output"},
 		{"help", "?", "help", "keybinding cheat-sheet"},
 		{"mode", "s", "toggle mode", "switch chat / steering"},
@@ -1122,6 +1125,8 @@ func (m Model) execPalette(id string) (tea.Model, tea.Cmd) {
 	case "statusbar":
 		m.overlay = OverlayStatusbar
 		m.sbIndex = 0
+	case "rail":
+		m.railHidden = !m.railHidden
 	case "actions":
 		m.toggleInlineActions()
 	case "help":
@@ -1164,6 +1169,11 @@ func (m *Model) backspace() {
 	m.inputCursor = c - 1
 }
 
+// cycleLauncherWf advances the idle launch target: 0 = chat, 1..N = workflows[i-1], wrapping.
+func (m *Model) cycleLauncherWf() {
+	m.launcherWf = (m.launcherWf + 1) % (len(m.workflows) + 1)
+}
+
 func (m *Model) cycleChatMode() {
 	if m.chatMode == ChatModeChat {
 		m.chatMode = ChatModeSteering
@@ -1211,6 +1221,20 @@ func (m Model) submit() (tea.Model, tea.Cmd) {
 			m.beginIntent(m.workflows[m.wfIndex])
 			return m, nil
 		}
+		// Launcher: a workflow is Tab-selected → start it with the typed text as its brief
+		// (empty brief is allowed, like the intent flow). The server makes the session; we
+		// focus it when its events arrive (pendingWorkflowFocus).
+		if m.launcherWf > 0 && m.launcherWf <= len(m.workflows) {
+			wf := m.workflows[m.launcherWf-1]
+			m.recordInput(text)
+			m.client.Send(protocol.StartSession(wf.ID, text))
+			m.clearInput()
+			m.inputMode = ModeRouter
+			m.editMode = ModeNormal
+			m.pendingWorkflowFocus = true
+			m.launcherWf = 0
+			return m, nil
+		}
 		// Entering an already-selected session (blank submit).
 		if text == "" && m.selectedID != "" {
 			m.sessionEntered = true