feat(tui-go): workflow-propose choice panel

Render a workflow.proposed frame as a single-select picker with a manual-answer
slot: ↑↓/jk to choose, enter to launch, e for custom, esc to peek away. Picking
a candidate sends StartSession (and focuses the launched session); the custom
slot continues the conversation via ChatInput. Reuses the modal helpers from the
clarification view.

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

@@ -58,6 +58,9 @@ func (m Model) View() string {
 	if m.displayState() == StateClarification {
 		return m.center(m.clarificationModal())
 	}
+	if m.displayState() == StateWorkflowPropose {
+		return m.center(m.proposeModal())
+	}
 	if m.overlay != OverlayNone {
 		return m.renderOverlay(base)
 	}
@@ -224,6 +227,9 @@ func (m Model) renderFooter() string {
 	case m.displayState() == StateClarification:
 		// The question form owns its keys; the footer mirrors the essentials.
 		hints = []string{hint("←→", "option"), hint("↑↓", "question"), hint("spc", "select"), hint("enter", "submit"), hint("esc", "later")}
+	case m.displayState() == StateWorkflowPropose:
+		// The picker owns its keys; the footer mirrors the essentials.
+		hints = []string{hint("↑↓", "choose"), hint("enter", "launch"), hint("e", "custom"), hint("esc", "later")}
 	case m.displayState() == StateIdle:
 		if nrw {
 			hints = []string{hint("i", "name"), hint("/", "filter"), hint("w", "wf"), hint("p", "cmds"), hint("q", "quit")}