Fix setup wizard and installer for fresh-install flow

- setup_manager: fall back to update_password if admin already exists
  (installer bootstrap creates admin; wizard now updates rather than fails)
- install.sh: chown repo to SUDO_USER instead of pic user so the
  invoking operator can run make update without git safe.directory errors
- test: update mock to also stub update_password when testing total auth failure

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

api/setup_manager.py

@@ -168,14 +168,19 @@ class SetupManager:
             if self.is_setup_complete():
                 return {'success': False, 'errors': ['Setup has already been completed.']}
 
-            # ── create admin user ──────────────────────────────────────────
+            # ── create or update admin user ────────────────────────────────
+            # The installer may have bootstrapped an admin account from a
+            # generated password. The wizard's job is to set the real password,
+            # so update it if the account already exists.
             ok = self.auth_manager.create_user(
                 username='admin',
                 password=password,
                 role='admin',
             )
             if not ok:
-                return {'success': False, 'errors': ['Failed to create admin user. The username may already exist.']}
+                ok = self.auth_manager.update_password('admin', password)
+            if not ok:
+                return {'success': False, 'errors': ['Failed to set admin password.']}
 
             # ── persist identity fields ────────────────────────────────────
             self.config_manager.set_identity_field('cell_name', cell_name)