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/db/links_test.go

@@ -223,3 +223,50 @@ func TestSyncLinks_DeletedSourceHidden(t *testing.T) {
 		t.Fatalf("soft-deleted source should not appear in backlinks, got %d", len(backlinks))
 	}
 }
+
+func TestResolveLink_TitleMatch(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	title := "nginx config"
+	target := &Entity{Body: "proxy_pass details", Title: &title, Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, target); err != nil {
+		t.Fatal(err)
+	}
+
+	resolved, err := s.ResolveLink(ctx, "nginx config")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if resolved.ID != target.ID {
+		t.Errorf("resolved ID = %s, want %s", resolved.ID, target.ID)
+	}
+}
+
+func TestResolveLink_BodyFallback(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	target := &Entity{Body: "deploy staging checklist", Glyph: "note", Tags: []string{}}
+	if err := s.Create(ctx, target); err != nil {
+		t.Fatal(err)
+	}
+
+	resolved, err := s.ResolveLink(ctx, "deploy staging")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if resolved.ID != target.ID {
+		t.Errorf("resolved ID = %s, want %s", resolved.ID, target.ID)
+	}
+}
+
+func TestResolveLink_NotFound(t *testing.T) {
+	s := testStore(t)
+	ctx := context.Background()
+
+	_, err := s.ResolveLink(ctx, "nonexistent entry")
+	if err != ErrNotFound {
+		t.Errorf("expected ErrNotFound, got %v", err)
+	}
+}