fix: wire handler layer in main.go and fix migration issues

cmd/server/main.go: replace stub router with full wiring —
  UserRepo, SessionRepo, AuthService, AuthMiddleware, AuthHandler,
  NewRouter; use postgres.NewPool instead of pgxpool.New directly.

migrations/001_init_schemas.sql: wrap uuid_v7 and uuid_extract_timestamp
  function bodies with goose StatementBegin/End so semicolons inside
  dollar-quoted strings are not treated as statement separators.

migrations/007_seed_data.sql: add seed admin user (admin/admin,
  bcrypt cost 10, is_admin=true, can_create=true) for manual testing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/migrations/007_seed_data.sql

@@ -26,7 +26,11 @@ INSERT INTO activity.action_types (name) VALUES
     -- Sessions
     ('session_terminate');
 
+INSERT INTO core.users (name, password, is_admin, can_create) VALUES
+    ('admin', '$2a$10$zk.VTFjRRxbkTE7cKfc7KOWeZfByk1VEkbkgZMJggI1fFf.yDEHZy', true, true);
+
 -- +goose Down
 
+DELETE FROM core.users WHERE name = 'admin';
 DELETE FROM activity.action_types;
 DELETE FROM core.object_types;