feat(workspace): journal with one note per day and a calendar

- journal_days (migration 8) maps a person's day to an ordinary note;
  GET /journal lists the days, POST /journal/{date} opens or creates one
- the journal sits on top of the notes sidebar: days below each other
  (today first, older ones load while scrolling), a calendar with month
  and year picker follows the day in view and jumps to any day
- the header shares the day in view; journal notes stay out of the folder
  tree; can be switched off per device under Darstellung

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/storage/journal.go

@@ -0,0 +1,65 @@
+package storage
+
+import (
+	"database/sql"
+	"errors"
+)
+
+// Journal: one note per person and day. The notes are ordinary documents (sharing, search, sync work as
+// usual); this table only remembers which note belongs to which day.
+
+type JournalDay struct {
+	Date  string `json:"date"` // YYYY-MM-DD
+	DocID string `json:"docId"`
+	Empty bool   `json:"empty"` // no text yet (the journal still shows today and days jumped to)
+}
+
+func (s *Store) migrateJournal() error {
+	return s.execInTx(
+		stmt(`CREATE TABLE IF NOT EXISTS journal_days (
+			user_id TEXT NOT NULL,
+			day TEXT NOT NULL,
+			doc_id TEXT NOT NULL,
+			PRIMARY KEY (user_id, day)
+		)`),
+		stmt(`CREATE INDEX IF NOT EXISTS idx_journal_days_doc ON journal_days(doc_id)`),
+	)
+}
+
+// JournalDays lists the user's days whose note still exists (not in the trash), newest first.
+func (s *Store) JournalDays(userID string) ([]JournalDay, error) {
+	rows, err := s.db.Query(`SELECT j.day, j.doc_id, TRIM(d.content) = ''
+		FROM journal_days j JOIN documents d ON d.id = j.doc_id
+		WHERE j.user_id = ? AND d.is_archived = 0
+		ORDER BY j.day DESC`, userID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	days := []JournalDay{}
+	for rows.Next() {
+		var d JournalDay
+		if err := rows.Scan(&d.Date, &d.DocID, &d.Empty); err != nil {
+			return nil, err
+		}
+		days = append(days, d)
+	}
+	return days, rows.Err()
+}
+
+// JournalDocID returns the note of a day; "" when there is none or it was moved to the trash.
+func (s *Store) JournalDocID(userID, day string) (string, error) {
+	var docID string
+	err := s.db.QueryRow(`SELECT j.doc_id FROM journal_days j JOIN documents d ON d.id = j.doc_id
+		WHERE j.user_id = ? AND j.day = ? AND d.is_archived = 0`, userID, day).Scan(&docID)
+	if errors.Is(err, sql.ErrNoRows) {
+		return "", nil
+	}
+	return docID, err
+}
+
+func (s *Store) SetJournalDay(userID, day, docID string) error {
+	_, err := s.db.Exec(`INSERT INTO journal_days (user_id, day, doc_id) VALUES (?, ?, ?)
+		ON CONFLICT(user_id, day) DO UPDATE SET doc_id = excluded.doc_id`, userID, day, docID)
+	return err
+}