feat(db): add wiki-link extraction, resolution, and backlinks

[[wiki-links]] in entry bodies are extracted at save time, resolved
to entity IDs (title match first, body substring fallback), and
stored in entity_links junction table. Backlinks surface in TUI
detail view showing entries that link to the current entry.

Schema migration v5 adds entity_links with CASCADE/SET NULL
semantics. Links sync on Create, Update, and Absorb.

internal/tui/commands.go

@@ -55,6 +55,10 @@ type stepsPersistedMsg struct{}
 
 type templateCopiedMsg struct{}
 
+type backlinksLoadedMsg struct {
+	backlinks []db.Backlink
+}
+
 type tagsLoadedMsg struct {
 	tags []db.TagCount
 }
@@ -194,6 +198,16 @@ func loadTags(store *db.Store) tea.Cmd {
 	}
 }
 
+func loadBacklinks(store *db.Store, entityID string) tea.Cmd {
+	return func() tea.Msg {
+		backlinks, err := store.LoadBacklinks(context.Background(), entityID)
+		if err != nil {
+			return errMsg{err}
+		}
+		return backlinksLoadedMsg{backlinks}
+	}
+}
+
 func loadRailTags(store *db.Store) tea.Cmd {
 	return func() tea.Msg {
 		tags, err := store.ListTags(context.Background(), false)

internal/tui/detail.go

@@ -21,13 +21,14 @@ const (
 )
 
 type detailModel struct {
-	entity *db.Entity
-	scroll int
-	height int
-	width  int
-	mode   detailMode
-	run    runModel
-	fill   fillModel
+	entity    *db.Entity
+	backlinks []db.Backlink
+	scroll    int
+	height    int
+	width     int
+	mode      detailMode
+	run       runModel
+	fill      fillModel
 }
 
 func newDetailModel() detailModel {
@@ -36,6 +37,7 @@ func newDetailModel() detailModel {
 
 func (d *detailModel) setEntity(e *db.Entity) {
 	d.entity = e
+	d.backlinks = nil
 	d.scroll = 0
 	d.mode = detailPreview
 }
@@ -144,6 +146,25 @@ func (d detailModel) previewView(width int) string {
 		b.WriteString("\n")
 	}
 
+	if len(d.backlinks) > 0 {
+		b.WriteString("\n")
+		b.WriteString(detailLabelStyle.Render("  ← backlinks"))
+		b.WriteString("\n")
+		for _, bl := range d.backlinks {
+			label := bl.Body
+			if bl.Title != nil {
+				label = *bl.Title
+			} else if len(label) > 40 {
+				label = label[:40] + "…"
+			}
+			line := "    " + backlinkStyle.Render(label)
+			if bl.LinkText != "" {
+				line += " " + hintDescStyle.Render("(as \""+bl.LinkText+"\")")
+			}
+			b.WriteString(line + "\n")
+		}
+	}
+
 	b.WriteString("\n")
 	meta := fmt.Sprintf("created  %s", e.CreatedAt.Format(time.DateTime))
 	if e.ModifiedAt != e.CreatedAt {

internal/tui/model.go

@@ -287,6 +287,12 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		m.detail.mode = detailPreview
 		return m, tea.Batch(loadEntities(m.store, m.listParams()), m.setStatus("copied resolved"))
 
+	case backlinksLoadedMsg:
+		if m.detail.entity != nil {
+			m.detail.backlinks = msg.backlinks
+		}
+		return m, nil
+
 	case tagsLoadedMsg:
 		m.filter.setTags(msg.tags)
 		m.tagRail.setTags(msg.tags)
@@ -865,6 +871,7 @@ func (m model) updateBrowse(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 				} else {
 					m.state = stateDetail
 				}
+				return m, loadBacklinks(m.store, e.ID)
 			}
 		}
 		return m, nil
@@ -1212,6 +1219,7 @@ func (m model) selectedEntity() *db.Entity {
 func (m model) reloadDetail(id string) tea.Cmd {
 	return tea.Batch(
 		loadEntities(m.store, m.listParams()),
+		loadBacklinks(m.store, id),
 		func() tea.Msg {
 			e, err := m.store.Get(context.Background(), id)
 			if err != nil {

internal/tui/styles.go

@@ -43,6 +43,7 @@ var (
 	stumbleAgeStyle     lipgloss.Style
 	acSelectedStyle     lipgloss.Style
 	acItemStyle         lipgloss.Style
+	backlinkStyle       lipgloss.Style
 )
 
 func init() {
@@ -100,4 +101,5 @@ func applyTheme() {
 	stumbleAgeStyle = lipgloss.NewStyle().Foreground(remind)
 	acSelectedStyle = lipgloss.NewStyle().Foreground(accent).Bold(true)
 	acItemStyle = lipgloss.NewStyle().Foreground(muted)
+	backlinkStyle = lipgloss.NewStyle().Foreground(muted)
 }