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/migrations/001_initial.sql

@@ -0,0 +1,61 @@
+-- +migrate Up
+CREATE TABLE entries (
+  id            TEXT PRIMARY KEY,
+  start_time    INTEGER NOT NULL,
+  end_time      INTEGER,
+  auto_stopped  INTEGER NOT NULL DEFAULT 0,
+  note          TEXT,
+  day_key       TEXT NOT NULL,
+  updated_at    INTEGER NOT NULL,
+  deleted_at    INTEGER
+);
+CREATE INDEX idx_entries_day ON entries(day_key);
+
+CREATE TABLE closed_days (
+  day_key       TEXT PRIMARY KEY,
+  start_time    INTEGER,
+  end_time      INTEGER,
+  worked_ms     INTEGER NOT NULL,
+  kind          TEXT NOT NULL,
+  closed_at     INTEGER NOT NULL,
+  updated_at    INTEGER NOT NULL
+);
+
+CREATE TABLE closed_weeks (
+  week_key      TEXT PRIMARY KEY,
+  expected_ms   INTEGER NOT NULL,
+  worked_ms     INTEGER NOT NULL,
+  delta_ms      INTEGER NOT NULL,
+  closed_at     INTEGER NOT NULL,
+  updated_at    INTEGER NOT NULL
+);
+
+CREATE TABLE settings_history (
+  id              INTEGER PRIMARY KEY AUTOINCREMENT,
+  effective_from  TEXT NOT NULL,
+  hours_per_week  REAL NOT NULL,
+  workdays_mask   INTEGER NOT NULL DEFAULT 31,
+  timezone        TEXT NOT NULL DEFAULT 'UTC',
+  created_at      INTEGER NOT NULL
+);
+
+CREATE TABLE sync_log (
+  entity        TEXT NOT NULL,
+  entity_id     TEXT NOT NULL,
+  op            TEXT NOT NULL,
+  version       INTEGER NOT NULL,
+  payload       TEXT NOT NULL,
+  PRIMARY KEY (entity, entity_id, version)
+);
+
+-- seed default settings
+INSERT INTO settings_history (effective_from, hours_per_week, workdays_mask, timezone, created_at)
+VALUES ('2000-01-01', 40.0, 31, 'UTC', unixepoch() * 1000);
+
+-- +migrate Down
+DROP TABLE IF EXISTS sync_log;
+DROP TABLE IF EXISTS settings_history;
+DROP TABLE IF EXISTS closed_weeks;
+DROP TABLE IF EXISTS closed_days;
+DROP INDEX IF EXISTS idx_entries_day;
+DROP TABLE IF EXISTS entries;

internal/store/migrations/002_balance_adjustments.sql

@@ -0,0 +1,14 @@
+-- +migrate Up
+CREATE TABLE balance_adjustments (
+  id           TEXT PRIMARY KEY,
+  delta_ms     INTEGER NOT NULL,
+  note         TEXT NOT NULL DEFAULT '',
+  effective_at INTEGER NOT NULL,
+  created_at   INTEGER NOT NULL,
+  updated_at   INTEGER NOT NULL
+);
+CREATE INDEX idx_balance_adjustments_effective_at ON balance_adjustments(effective_at);
+
+-- +migrate Down
+DROP INDEX IF EXISTS idx_balance_adjustments_effective_at;
+DROP TABLE IF EXISTS balance_adjustments;