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/db.go

@@ -3,15 +3,18 @@ package store
 import (
 	"context"
 	"database/sql"
-	_ "embed"
 	"fmt"
+	"io/fs"
+	"sort"
 	"strings"
 
 	_ "modernc.org/sqlite"
+
+	"embed"
 )
 
-//go:embed 001_initial.sql
-var schema string
+//go:embed migrations/*.sql
+var migrationsFS embed.FS
 
 // Open opens (or creates) the SQLite database at path and runs migrations.
 func Open(path string) (*sql.DB, error) {
@@ -31,22 +34,51 @@ func Open(path string) (*sql.DB, error) {
 	return db, nil
 }
 
-// migrate runs embedded SQL migrations. Simple single-file approach: we track
-// a user_version pragma and apply the schema once if version == 0.
+// migrate applies all SQL migration files in migrations/ in filename order.
+// user_version tracks the last applied migration index (1-based).
 func migrate(db *sql.DB) error {
 	var version int
 	if err := db.QueryRow("PRAGMA user_version").Scan(&version); err != nil {
 		return err
 	}
-	if version >= 1 {
-		return nil
+
+	entries, err := fs.ReadDir(migrationsFS, "migrations")
+	if err != nil {
+		return fmt.Errorf("read migrations dir: %w", err)
 	}
 
+	// Sort by name so 001_*, 002_* apply in order.
+	sort.Slice(entries, func(i, j int) bool {
+		return entries[i].Name() < entries[j].Name()
+	})
+
 	ctx := context.Background()
 
-	// Strip migration comments and split into individual statements
-	stmts := splitStatements(schema)
-	for _, stmt := range stmts {
+	for i, entry := range entries {
+		migrationNum := i + 1 // 1-based
+		if version >= migrationNum {
+			continue
+		}
+
+		data, err := migrationsFS.ReadFile("migrations/" + entry.Name())
+		if err != nil {
+			return fmt.Errorf("read %s: %w", entry.Name(), err)
+		}
+
+		if err := applySchema(db, ctx, string(data)); err != nil {
+			return fmt.Errorf("migration %d (%s): %w", migrationNum, entry.Name(), err)
+		}
+
+		if _, err := db.ExecContext(ctx, fmt.Sprintf("PRAGMA user_version = %d", migrationNum)); err != nil {
+			return fmt.Errorf("set user_version = %d: %w", migrationNum, err)
+		}
+	}
+
+	return nil
+}
+
+func applySchema(db *sql.DB, ctx context.Context, sql string) error {
+	for _, stmt := range splitStatements(sql) {
 		stmt = strings.TrimSpace(stmt)
 		if stmt == "" {
 			continue
@@ -55,12 +87,6 @@ func migrate(db *sql.DB) error {
 			return fmt.Errorf("exec %q: %w", stmt[:min(len(stmt), 60)], err)
 		}
 	}
-
-	// PRAGMA user_version cannot be set inside a regular transaction in all SQLite versions;
-	// execute it as a standalone statement.
-	if _, err := db.ExecContext(ctx, "PRAGMA user_version = 1"); err != nil {
-		return err
-	}
 	return nil
 }