feat(auth): implement API key authentication and management

Introduce a new API key authentication mechanism to support service-to-service
communication (e.g., Airflow, CI/CD) without browser-based JWT login.

- Add `APIKey` model and `APIKeyPrincipal` dependency for RBAC.
- Implement `require_api_key_or_jwt` dependency with environment scoping.
- Add admin CRUD endpoints for API key lifecycle management.
- Add API key management UI in System Settings.
- Update maintenance API to support explicit `environment_id` and API key auth.
- Add i18n support for API keys and connection settings.
- Include Python and Bash usage examples in the `examples/` directory.
- Update technical specifications and documentation.

frontend/src/components/StartupEnvironmentWizard.svelte

@@ -1,6 +1,7 @@
 <!-- #region StartupEnvironmentWizard [C:3] [TYPE Component] [SEMANTICS wizard, environment, setup, onboarding, form] -->
 <!-- @BRIEF Component component: components/StartupEnvironmentWizard.svelte -->
 <!-- @LAYER UI -->
+<!-- @RATIONALE Fixed (1) missing connections.json locale — $t.connections?.name/user/pass rendered empty spans causing floating form fields. Created en/ru locales. (2) header bg-slate-50 created visible white strip at top in darkened modal overlay; changed to bg-white, border-b provides sufficient separation. -->
 <script>
   /**
    * @PURPOSE: Blocking startup wizard for creating the first Superset environment from zero-state screens.
@@ -114,7 +115,7 @@
 {#if open}
   <div class="fixed inset-0 z-50 flex items-center justify-center bg-slate-950/45 px-4 py-6 backdrop-blur-sm">
     <div class="w-full max-w-3xl overflow-hidden rounded-3xl border border-slate-200 bg-white shadow-2xl">
-      <div class="border-b border-slate-200 bg-slate-50 px-6 py-5">
+      <div class="border-b border-slate-200 bg-white px-6 py-5">
         <div class="flex items-start justify-between gap-4">
           <div>
             <p class="text-xs font-semibold uppercase tracking-[0.24em] text-sky-600">{$t.nav?.dashboards}</p>