Initial commit: Triple-C app, container, and CI

Tauri v2 desktop app (React/TypeScript + Rust) for managing
containerized Claude Code environments. Includes Gitea Actions
workflow for building and pushing the sandbox container image,
and a BUILDING.md guide for manual app builds on Linux and Windows.

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

app/src/components/settings/SettingsPanel.tsx

@@ -0,0 +1,14 @@
+import ApiKeyInput from "./ApiKeyInput";
+import DockerSettings from "./DockerSettings";
+
+export default function SettingsPanel() {
+  return (
+    <div className="p-4 space-y-6">
+      <h2 className="text-xs font-semibold uppercase text-[var(--text-secondary)]">
+        Settings
+      </h2>
+      <ApiKeyInput />
+      <DockerSettings />
+    </div>
+  );
+}