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/service/week_service.go

@@ -11,13 +11,21 @@ import (
 	"github.com/wotra/wotra/internal/store"
 )
 
+// Sentinel errors for balance adjustments.
+var (
+	ErrZeroAdjustment    = errors.New("delta_ms must be non-zero")
+	ErrAdjustmentNotFound = errors.New("balance adjustment not found")
+)
+
 // WeekService handles closing weeks and computing overtime/undertime.
 type WeekService struct {
-	closedDays  *store.ClosedDayStore
-	closedWeeks *store.ClosedWeekStore
-	entries     *store.EntryStore
-	settings    *store.SettingsStore
-	db          interface {
+	closedDays   *store.ClosedDayStore
+	closedWeeks  *store.ClosedWeekStore
+	adjustments  *store.BalanceAdjustmentStore
+	syncStore    *store.SyncStore
+	entries      *store.EntryStore
+	settings     *store.SettingsStore
+	db           interface {
 		QueryRowContext(ctx context.Context, query string, args ...interface{}) *sql.Row
 	}
 	rawDB *sql.DB
@@ -29,12 +37,16 @@ func NewWeekService(
 	closedWeeks *store.ClosedWeekStore,
 	entries *store.EntryStore,
 	settings *store.SettingsStore,
+	adjustments *store.BalanceAdjustmentStore,
+	syncStore *store.SyncStore,
 	rawDB *sql.DB,
 	tz *time.Location,
 ) *WeekService {
 	return &WeekService{
 		closedDays:  closedDays,
 		closedWeeks: closedWeeks,
+		adjustments: adjustments,
+		syncStore:   syncStore,
 		entries:     entries,
 		settings:    settings,
 		rawDB:       rawDB,
@@ -44,17 +56,78 @@ func NewWeekService(
 
 // BalanceResult holds the overall overtime/undertime balance across all closed weeks.
 type BalanceResult struct {
-	TotalDeltaMs    int64 `json:"total_delta_ms"`
-	ClosedWeekCount int   `json:"closed_week_count"`
+	TotalDeltaMs        int64 `json:"total_delta_ms"`
+	WeeksDeltaMs        int64 `json:"weeks_delta_ms"`
+	AdjustmentsDeltaMs  int64 `json:"adjustments_delta_ms"`
+	ClosedWeekCount     int   `json:"closed_week_count"`
+	AdjustmentCount     int   `json:"adjustment_count"`
 }
 
-// Balance returns the sum of delta_ms across all closed weeks.
+// Balance returns the combined overtime balance: closed weeks + manual adjustments.
 func (s *WeekService) Balance(ctx context.Context) (BalanceResult, error) {
-	total, count, err := s.closedWeeks.SumDelta(ctx)
+	weeksTotal, weekCount, err := s.closedWeeks.SumDelta(ctx)
 	if err != nil {
 		return BalanceResult{}, err
 	}
-	return BalanceResult{TotalDeltaMs: total, ClosedWeekCount: count}, nil
+	adjTotal, adjCount, err := s.adjustments.SumDelta(ctx)
+	if err != nil {
+		return BalanceResult{}, err
+	}
+	return BalanceResult{
+		TotalDeltaMs:       weeksTotal + adjTotal,
+		WeeksDeltaMs:       weeksTotal,
+		AdjustmentsDeltaMs: adjTotal,
+		ClosedWeekCount:    weekCount,
+		AdjustmentCount:    adjCount,
+	}, nil
+}
+
+// ListAdjustments returns all balance adjustments ordered by effective_at DESC.
+func (s *WeekService) ListAdjustments(ctx context.Context) ([]*domain.BalanceAdjustment, error) {
+	return s.adjustments.List(ctx)
+}
+
+// CreateAdjustment creates and sync-logs a new balance adjustment.
+func (s *WeekService) CreateAdjustment(ctx context.Context, a *domain.BalanceAdjustment) (*domain.BalanceAdjustment, error) {
+	if a.DeltaMs == 0 {
+		return nil, ErrZeroAdjustment
+	}
+	if err := s.adjustments.Create(ctx, a); err != nil {
+		return nil, err
+	}
+	_ = s.syncStore.LogBalanceAdjustment(ctx, a) // best-effort
+	return a, nil
+}
+
+// UpdateAdjustment updates and sync-logs an existing balance adjustment.
+func (s *WeekService) UpdateAdjustment(ctx context.Context, a *domain.BalanceAdjustment) (*domain.BalanceAdjustment, error) {
+	if a.DeltaMs == 0 {
+		return nil, ErrZeroAdjustment
+	}
+	if err := s.adjustments.Update(ctx, a); err != nil {
+		if errors.Is(err, store.ErrAdjustmentNotFound) {
+			return nil, ErrAdjustmentNotFound
+		}
+		return nil, err
+	}
+	got, err := s.adjustments.GetByID(ctx, a.ID)
+	if err != nil {
+		return nil, err
+	}
+	_ = s.syncStore.LogBalanceAdjustment(ctx, got) // best-effort
+	return got, nil
+}
+
+// DeleteAdjustment deletes and sync-logs a balance adjustment.
+func (s *WeekService) DeleteAdjustment(ctx context.Context, id string) error {
+	if err := s.adjustments.Delete(ctx, id); err != nil {
+		if errors.Is(err, store.ErrAdjustmentNotFound) {
+			return ErrAdjustmentNotFound
+		}
+		return err
+	}
+	_ = s.syncStore.LogBalanceAdjustmentDelete(ctx, id) // best-effort
+	return nil
 }
 
 // WeekDayKeysExported is exported for testing.