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/handler/week_handler.go

@@ -1,14 +1,18 @@
 package handler
 
 import (
+	"encoding/json"
 	"errors"
 	"net/http"
+	"time"
 
 	"github.com/go-chi/chi/v5"
+	"github.com/google/uuid"
+	"github.com/wotra/wotra/internal/domain"
 	"github.com/wotra/wotra/internal/service"
 )
 
-// WeekHandler serves /api/weeks routes.
+// WeekHandler serves /api/weeks and /api/balance/adjustments routes.
 type WeekHandler struct {
 	svc *service.WeekService
 }
@@ -22,6 +26,11 @@ func (h *WeekHandler) Routes(r chi.Router) {
 	r.Get("/weeks/balance", h.Balance)
 	r.Post("/weeks/{week_key}/close", h.Close)
 	r.Delete("/weeks/{week_key}/close", h.Reopen)
+
+	r.Get("/balance/adjustments", h.ListAdjustments)
+	r.Post("/balance/adjustments", h.CreateAdjustment)
+	r.Put("/balance/adjustments/{id}", h.UpdateAdjustment)
+	r.Delete("/balance/adjustments/{id}", h.DeleteAdjustment)
 }
 
 // Balance GET /api/weeks/balance
@@ -90,3 +99,107 @@ func (h *WeekHandler) Reopen(w http.ResponseWriter, r *http.Request) {
 	}
 	w.WriteHeader(http.StatusNoContent)
 }
+
+// ── Balance adjustments ───────────────────────────────────────────────────────
+
+// ListAdjustments GET /api/balance/adjustments
+func (h *WeekHandler) ListAdjustments(w http.ResponseWriter, r *http.Request) {
+	list, err := h.svc.ListAdjustments(r.Context())
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	if list == nil {
+		writeJSON(w, http.StatusOK, []*domain.BalanceAdjustment{})
+		return
+	}
+	writeJSON(w, http.StatusOK, list)
+}
+
+type adjustmentRequest struct {
+	DeltaMs     int64  `json:"delta_ms"`
+	Note        string `json:"note"`
+	EffectiveAt *int64 `json:"effective_at"` // optional; defaults to now
+}
+
+// CreateAdjustment POST /api/balance/adjustments
+func (h *WeekHandler) CreateAdjustment(w http.ResponseWriter, r *http.Request) {
+	var req adjustmentRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid JSON")
+		return
+	}
+	now := time.Now().UnixMilli()
+	effectiveAt := now
+	if req.EffectiveAt != nil {
+		effectiveAt = *req.EffectiveAt
+	}
+	a := &domain.BalanceAdjustment{
+		ID:          uuid.New().String(),
+		DeltaMs:     req.DeltaMs,
+		Note:        req.Note,
+		EffectiveAt: effectiveAt,
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+	created, err := h.svc.CreateAdjustment(r.Context(), a)
+	if err != nil {
+		if errors.Is(err, service.ErrZeroAdjustment) {
+			writeError(w, http.StatusBadRequest, err.Error())
+			return
+		}
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	writeJSON(w, http.StatusCreated, created)
+}
+
+// UpdateAdjustment PUT /api/balance/adjustments/{id}
+func (h *WeekHandler) UpdateAdjustment(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	var req adjustmentRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid JSON")
+		return
+	}
+	now := time.Now().UnixMilli()
+	effectiveAt := now
+	if req.EffectiveAt != nil {
+		effectiveAt = *req.EffectiveAt
+	}
+	a := &domain.BalanceAdjustment{
+		ID:          id,
+		DeltaMs:     req.DeltaMs,
+		Note:        req.Note,
+		EffectiveAt: effectiveAt,
+		UpdatedAt:   now,
+	}
+	updated, err := h.svc.UpdateAdjustment(r.Context(), a)
+	if err != nil {
+		switch {
+		case errors.Is(err, service.ErrZeroAdjustment):
+			writeError(w, http.StatusBadRequest, err.Error())
+		case errors.Is(err, service.ErrAdjustmentNotFound):
+			writeError(w, http.StatusNotFound, err.Error())
+		default:
+			writeError(w, http.StatusInternalServerError, err.Error())
+		}
+		return
+	}
+	writeJSON(w, http.StatusOK, updated)
+}
+
+// DeleteAdjustment DELETE /api/balance/adjustments/{id}
+func (h *WeekHandler) DeleteAdjustment(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	if err := h.svc.DeleteAdjustment(r.Context(), id); err != nil {
+		switch {
+		case errors.Is(err, service.ErrAdjustmentNotFound):
+			writeError(w, http.StatusNotFound, err.Error())
+		default:
+			writeError(w, http.StatusInternalServerError, err.Error())
+		}
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}