Add balance adjustments (M8)

- New balance_adjustments table with CRUD store, sync logging, and service methods
- SQL migrations restructured: embed fs.FS from internal/store/migrations/, apply in order via user_version
- WeekService.Balance combines closed-weeks delta + adjustments delta; BalanceSummary breakdown
- Four REST routes: GET/POST /api/balance/adjustments, PUT/DELETE /api/balance/adjustments/{id}
- Dexie schema v2 + sync apply cases for balance_adjustments
- API client: BalanceAdjustment type, balance namespace (list/create/update/delete)
- utils: composeDeltaMs / decomposeDeltaMs helpers + 8 new Vitest tests (19 total, all passing)
- History page: balance card breakdown line + full adjustments section with inline add/edit/delete

internal/store/balance_adjustment_store.go

@@ -0,0 +1,100 @@
+package store
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+
+	"github.com/wotra/wotra/internal/domain"
+)
+
+// BalanceAdjustmentStore handles persistence for balance_adjustments.
+type BalanceAdjustmentStore struct {
+	db *sql.DB
+}
+
+func NewBalanceAdjustmentStore(db *sql.DB) *BalanceAdjustmentStore {
+	return &BalanceAdjustmentStore{db: db}
+}
+
+func (s *BalanceAdjustmentStore) Create(ctx context.Context, a *domain.BalanceAdjustment) error {
+	_, err := s.db.ExecContext(ctx,
+		`INSERT INTO balance_adjustments (id, delta_ms, note, effective_at, created_at, updated_at)
+		 VALUES (?, ?, ?, ?, ?, ?)`,
+		a.ID, a.DeltaMs, a.Note, a.EffectiveAt, a.CreatedAt, a.UpdatedAt,
+	)
+	return err
+}
+
+func (s *BalanceAdjustmentStore) Update(ctx context.Context, a *domain.BalanceAdjustment) error {
+	res, err := s.db.ExecContext(ctx,
+		`UPDATE balance_adjustments SET delta_ms=?, note=?, effective_at=?, updated_at=? WHERE id=?`,
+		a.DeltaMs, a.Note, a.EffectiveAt, a.UpdatedAt, a.ID,
+	)
+	if err != nil {
+		return err
+	}
+	n, _ := res.RowsAffected()
+	if n == 0 {
+		return ErrAdjustmentNotFound
+	}
+	return nil
+}
+
+func (s *BalanceAdjustmentStore) Delete(ctx context.Context, id string) error {
+	res, err := s.db.ExecContext(ctx, `DELETE FROM balance_adjustments WHERE id=?`, id)
+	if err != nil {
+		return err
+	}
+	n, _ := res.RowsAffected()
+	if n == 0 {
+		return ErrAdjustmentNotFound
+	}
+	return nil
+}
+
+func (s *BalanceAdjustmentStore) GetByID(ctx context.Context, id string) (*domain.BalanceAdjustment, error) {
+	row := s.db.QueryRowContext(ctx,
+		`SELECT id, delta_ms, note, effective_at, created_at, updated_at
+		 FROM balance_adjustments WHERE id=?`, id)
+	var a domain.BalanceAdjustment
+	err := row.Scan(&a.ID, &a.DeltaMs, &a.Note, &a.EffectiveAt, &a.CreatedAt, &a.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrAdjustmentNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &a, nil
+}
+
+// List returns all adjustments ordered by effective_at DESC.
+func (s *BalanceAdjustmentStore) List(ctx context.Context) ([]*domain.BalanceAdjustment, error) {
+	rows, err := s.db.QueryContext(ctx,
+		`SELECT id, delta_ms, note, effective_at, created_at, updated_at
+		 FROM balance_adjustments ORDER BY effective_at DESC`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var result []*domain.BalanceAdjustment
+	for rows.Next() {
+		var a domain.BalanceAdjustment
+		if err := rows.Scan(&a.ID, &a.DeltaMs, &a.Note, &a.EffectiveAt, &a.CreatedAt, &a.UpdatedAt); err != nil {
+			return nil, err
+		}
+		result = append(result, &a)
+	}
+	return result, rows.Err()
+}
+
+// SumDelta returns the sum of delta_ms and row count across all adjustments.
+func (s *BalanceAdjustmentStore) SumDelta(ctx context.Context) (totalDeltaMs int64, count int, err error) {
+	err = s.db.QueryRowContext(ctx,
+		`SELECT COALESCE(SUM(delta_ms), 0), COUNT(*) FROM balance_adjustments`,
+	).Scan(&totalDeltaMs, &count)
+	return
+}
+
+// ErrAdjustmentNotFound is returned when no balance_adjustment row matches the given ID.
+var ErrAdjustmentNotFound = errors.New("balance adjustment not found")