Today view and Inbox section: dynamic query, not stored sections

- ListTodayView() on backend: queries nodes created or updated today
  using local timezone day boundaries
- todayBoundaries() helper returns start/end of current day in RFC3339
- Section validation: Create() rejects today and inbox as node sections
- validSections moved from repository.go to types.go with IsValidSection
  and IsServiceSection helpers
- Frontend selectSection('today') calls ListTodayView instead of
  ListNodesBySection('today')
- FAB (create node) hidden in today and inbox sections
- CreateNode in app.go guarded against today/inbox sections
- types.go: today/inbox defined as service sections (sidebar only)

internal/core/nodes/repository.go

@@ -50,16 +50,10 @@ func now() string {
 	return time.Now().UTC().Format(time.RFC3339)
 }
 
-// --- CRUD ---
-
-// Valid sections for root-level nodes.
-var validSections = map[string]struct{}{
-	"clients": {}, "projects": {}, "recipes": {}, "documents": {}, "archive": {},
-}
-
 // Create inserts a root or child node.
 // parentID may be empty for root-level nodes.
-// For root nodes, section determines sidebar placement (may be empty → inbox).
+// For root nodes, section determines sidebar placement (may be empty = inbox).
+// section must be a valid section (clients, projects, etc.) or empty for inbox.
 func (r *Repository) Create(parentID, typ, title, section string) (*Node, error) {
 	if !IsValidType(typ) {
 		return nil, fmt.Errorf("invalid node type: %s", typ)
@@ -67,6 +61,9 @@ func (r *Repository) Create(parentID, typ, title, section string) (*Node, error)
 	if title == "" {
 		return nil, errors.New("title is required")
 	}
+	if section != "" && !IsValidSection(section) {
+		return nil, fmt.Errorf("invalid section: %s", section)
+	}
 
 	n := &Node{
 		ID:        util.UUID7(),
@@ -182,6 +179,39 @@ func (r *Repository) ListRoots(includeDeleted bool, section string) ([]Node, err
 	return scanNodes(rows)
 }
 
+// todayBoundaries returns RFC3339 start and end strings for the current day
+// in the local timezone (the server's timezone, which should match the user's).
+// TODO: accept a user timezone offset when multi-user support is added.
+func todayBoundaries() (string, string) {
+	now := time.Now()
+	y, m, d := now.Date()
+	start := time.Date(y, m, d, 0, 0, 0, 0, now.Location())
+	end := start.Add(24 * time.Hour)
+	return start.Format(time.RFC3339), end.Format(time.RFC3339)
+}
+
+// ListTodayNodes returns active root-level nodes created or updated today.
+// This is a dynamic view, not a section — it shows the day's activity.
+func (r *Repository) ListTodayNodes() ([]Node, error) {
+	start, end := todayBoundaries()
+	q := `SELECT id,parent_id,type,title,slug,path,section,sort_order,
+		created_at,updated_at,deleted_at,revision,device_id
+		FROM nodes
+		WHERE deleted_at IS NULL
+		AND (
+			(created_at >= ? AND created_at < ?)
+			OR
+			(updated_at >= ? AND updated_at < ?)
+		)
+		ORDER BY updated_at DESC, created_at DESC`
+	rows, err := r.db.Query(q, start, end, start, end)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	return scanNodes(rows)
+}
+
 // UpdateTitle changes title (slug is recomputed).
 func (r *Repository) UpdateTitle(id, title string) error {
 	if title == "" {

internal/core/nodes/types.go

@@ -35,12 +35,40 @@ var TypeSet = map[string]struct{}{
 	TypeLink:     {},
 }
 
+// Valid sections for root-level nodes.
+// today and inbox are service sections, not stored in nodes.section.
+var validSections = map[string]struct{}{
+	"clients":   {},
+	"projects":  {},
+	"recipes":   {},
+	"documents": {},
+	"archive":   {},
+}
+
+// serviceSections are sidebar entries that are not stored as node sections.
+var serviceSections = map[string]struct{}{
+	"today": {},
+	"inbox": {},
+}
+
 // IsValidType checks whether a type string is recognized.
 func IsValidType(t string) bool {
 	_, ok := TypeSet[t]
 	return ok
 }
 
+// IsValidSection returns true for sections that can be stored on a node.
+func IsValidSection(s string) bool {
+	_, ok := validSections[s]
+	return ok
+}
+
+// IsServiceSection returns true for sidebar-only sections (today, inbox).
+func IsServiceSection(s string) bool {
+	_, ok := serviceSections[s]
+	return ok
+}
+
 // Slugify converts a title into a filesystem-safe slug.
 // Examples:
 //