Add sync redesign with offline fallback (M9)

- Migration 003: adds logged_at to sync_log for TTL pruning; migrates
  settings_history to UUID TEXT PK with updated_at column
- SyncStore: Prune() deletes rows older than 30d and writes a '_pruned'
  marker at the boundary version; Pull() calls Prune lazily and returns
  ErrSyncStale (410) when the client's since_version is behind the marker
- sync_handler.go: GET /api/sync/pull?since=N; POST /api/sync/push with
  last-updated_at-wins conflict resolution for entries, balance_adjustments,
  settings_history; closed_days/closed_weeks skipped (server-only mutations)
- router.go: passes entryStore, adjustmentStore, settingsStore to SyncHandler
- settings_store.go: UUID PK, updated_at column, Upsert() for push path
- settings_service.go: generates UUID on create, sets updated_at on update
- settings_handler.go: ID params changed from int64 to string
- domain.go: Settings.ID string, Settings.UpdatedAt added
- client.ts: all mutation methods catch TypeError (offline) and fall back
  to Dexie write + outbox enqueue; crypto.randomUUID() for offline creates;
  Settings.id type changed to string
- db.ts: Dexie v3 — settings_history key path changed to string UUID;
  upgrade handler clears table for repopulation via pull
- sync.ts: real pushOutbox to POST /api/sync/push; pullChanges uses GET
  with ?since=N; 410 triggers coldStart() + retry; coldStart() wipes all
  tables and resets last_version
- 4 new Go store tests covering normal pull, stale client, empty prune,
  client-ahead-of-marker; all tests pass (store + service, 19 Vitest)

internal/handler/settings_handler.go

@@ -4,7 +4,6 @@ import (
 	"database/sql"
 	"errors"
 	"net/http"
-	"strconv"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/wotra/wotra/internal/service"
@@ -83,8 +82,8 @@ func (h *SettingsHandler) History(w http.ResponseWriter, r *http.Request) {
 
 // UpdateHistoryRow PUT /api/settings/history/{id}
 func (h *SettingsHandler) UpdateHistoryRow(w http.ResponseWriter, r *http.Request) {
-	id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
-	if err != nil {
+	id := chi.URLParam(r, "id")
+	if id == "" {
 		writeError(w, http.StatusBadRequest, "invalid id")
 		return
 	}
@@ -120,8 +119,8 @@ func (h *SettingsHandler) UpdateHistoryRow(w http.ResponseWriter, r *http.Reques
 
 // DeleteHistoryRow DELETE /api/settings/history/{id}
 func (h *SettingsHandler) DeleteHistoryRow(w http.ResponseWriter, r *http.Request) {
-	id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
-	if err != nil {
+	id := chi.URLParam(r, "id")
+	if id == "" {
 		writeError(w, http.StatusBadRequest, "invalid id")
 		return
 	}
@@ -138,4 +137,3 @@ func (h *SettingsHandler) DeleteHistoryRow(w http.ResponseWriter, r *http.Reques
 	}
 	w.WriteHeader(http.StatusNoContent)
 }
-