feat(tui): add link picker and navigation history

Press [ in detail view to open link picker showing all [[links]]
in the current entry. Enter follows a link, resolving by title
then body substring. Navigation history stack enables esc to pop
back through followed links before returning to list.

Adds Store.ResolveLink() for non-transactional link resolution
from the TUI layer.

internal/tui/model.go

@@ -24,6 +24,7 @@ const (
 	statePromote
 	stateAbsorb
 	stateStumble
+	stateLinkPicker
 )
 
 type viewMode int
@@ -90,6 +91,8 @@ type model struct {
 	stumble      stumbleModel
 	showHelp     bool
 	autocomplete autocompleteModel
+	linkPicker   linkPickerModel
+	navStack     []string
 
 	focus       focusPane
 	splitDetail bool
@@ -293,6 +296,11 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		}
 		return m, nil
 
+	case linkFollowedMsg:
+		m.detail.setEntity(msg.entity)
+		m.state = stateDetail
+		return m, loadBacklinks(m.store, msg.entity.ID)
+
 	case tagsLoadedMsg:
 		m.filter.setTags(msg.tags)
 		m.tagRail.setTags(msg.tags)
@@ -346,6 +354,8 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			return m.updateAbsorb(msg)
 		case stateStumble:
 			return m.updateStumble(msg)
+		case stateLinkPicker:
+			return m.updateLinkPicker(msg)
 		default:
 			return m.updateKeys(msg)
 		}
@@ -717,6 +727,19 @@ func (m model) updateBrowse(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 				}
 				return m, nil
 			}
+			if len(m.navStack) > 0 {
+				prevID := m.navStack[len(m.navStack)-1]
+				m.navStack = m.navStack[:len(m.navStack)-1]
+				return m, tea.Batch(
+					func() tea.Msg {
+						e, err := m.store.Get(context.Background(), prevID)
+						if err != nil {
+							return errMsg{err}
+						}
+						return linkFollowedMsg{e}
+					},
+				)
+			}
 			if m.isSplit() {
 				m.state = stateList
 				m.splitDetail = true
@@ -835,6 +858,14 @@ func (m model) updateBrowse(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 		}
 		return m, nil
 
+	case "[":
+		if m.state == stateDetail && m.detail.entity != nil && m.detail.mode == detailPreview {
+			m.linkPicker = newLinkPicker(m.detail.entity.Body)
+			m.state = stateLinkPicker
+			return m, nil
+		}
+		return m, nil
+
 	case "r":
 		if m.state == stateDetail && m.detail.entity != nil && m.detail.mode == detailPreview {
 			if m.detail.entity.CardType != nil && *m.detail.entity.CardType == db.CardChecklist {
@@ -927,6 +958,26 @@ func (m model) updateConfirm(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 	return m, nil
 }
 
+func (m model) updateLinkPicker(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
+	switch msg.String() {
+	case "esc", "q":
+		m.state = stateDetail
+		return m, nil
+	case "enter":
+		lt := m.linkPicker.selected()
+		if lt == "" {
+			return m, nil
+		}
+		if m.detail.entity != nil {
+			m.navStack = append(m.navStack, m.detail.entity.ID)
+		}
+		return m, followLink(m.store, lt)
+	default:
+		m.linkPicker = m.linkPicker.update(msg.String())
+		return m, nil
+	}
+}
+
 func (m model) updatePromote(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 	switch msg.String() {
 	case "esc", "q":
@@ -1045,6 +1096,8 @@ func (m model) View() string {
 		content = m.absorb.view(m.width)
 	case stateStumble:
 		content = m.stumble.view()
+	case stateLinkPicker:
+		content = m.linkPicker.view(m.width)
 	}
 
 	header := m.headerView()