feat(tui-go): idea board viewer

OverlayIdeas (opened with I, global/cross-session) lists the idea board in the
artifact-viewer shell: ↑↓ to move, x/d to remove (sends DiscardIdea, optimistic
drop), esc to close. Pull-based via ListIdeas -> idea.list.

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

@@ -0,0 +1,82 @@
+package app
+
+import (
+	"strings"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+// ideacard.go renders the cross-session idea board (OverlayIdeas): the ideas the router
+// captured while the operator rubber-ducked, each removable. Modeled on the artifact
+// viewer's list shell, but ideas are short notes so there is no separate content pane.
+
+// ideaListRows is how many idea rows fit in the board (the rest is title + hints).
+func (m Model) ideaListRows() int {
+	rows := m.height*70/100 - 5
+	if rows < 1 {
+		rows = 1
+	}
+	if rows > len(m.ideas) {
+		rows = len(m.ideas)
+	}
+	if rows < 1 {
+		rows = 1
+	}
+	return rows
+}
+
+func (m Model) ideasModal() string {
+	t := m.theme
+	w := m.modalWidth()
+
+	var b strings.Builder
+	b.WriteString(m.titleLine("ideas"))
+	if len(m.ideas) > 0 {
+		b.WriteString(mbg(t, "   ("+itoa(m.ideasIndex+1)+"/"+itoa(len(m.ideas))+")", t.P.Faint))
+	}
+	b.WriteString(mbg(t, "   · captured while rubber-ducking", t.P.Faint) + "\n\n")
+
+	if m.ideasLoading {
+		b.WriteString(mbg(t, "  loading…", t.P.Faint) + "\n")
+		b.WriteString("\n" + modalHints(t, [][2]string{{"esc", "close"}}))
+		return t.Overlay.Width(w).Render(b.String())
+	}
+	if len(m.ideas) == 0 {
+		b.WriteString(mbg(t, "  no ideas yet — they're saved as you think out loud with the router", t.P.Faint) + "\n")
+		b.WriteString("\n" + modalHints(t, [][2]string{{"esc", "close"}}))
+		return t.Overlay.Width(w).Render(b.String())
+	}
+
+	// Windowed list, keeping the selected row in view.
+	rows := m.ideaListRows()
+	off := 0
+	if len(m.ideas) > rows {
+		off = m.ideasIndex - rows/2
+		if off < 0 {
+			off = 0
+		}
+		if off > len(m.ideas)-rows {
+			off = len(m.ideas) - rows
+		}
+	}
+	end := off + rows
+	if end > len(m.ideas) {
+		end = len(m.ideas)
+	}
+	textW := w - 8
+	for i := off; i < end; i++ {
+		marker := mbg(t, "  ", t.P.BgPanel)
+		fg := t.P.Fg
+		if i == m.ideasIndex {
+			marker = lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.BgPanel).Render("▸ ")
+			fg = t.P.FgStrong
+		}
+		text := strings.ReplaceAll(m.ideas[i].Text, "\n", " ")
+		b.WriteString(marker + lipgloss.NewStyle().Foreground(fg).Background(t.P.BgPanel).Render(clip(text, textW)) + "\n")
+	}
+
+	b.WriteString("\n" + modalHints(t, [][2]string{
+		{"↑↓", "move"}, {"x", "remove"}, {"esc", "close"},
+	}))
+	return t.Overlay.Width(w).Render(b.String())
+}