feat: add v2 stack (backend, runner, ui-v2) with release workflow

- backend/: Go API server and runner binaries with PocketBase + MinIO storage
- ui-v2/: SvelteKit frontend rewrite
- docker-compose-new.yml: compose file for the v2 stack
- .gitea/workflows/release-v2.yaml: CI/CD for backend, runner, and ui-v2 Docker Hub images
- scripts/pb-init.sh: migrate from wget to curl, add superuser bootstrap for fresh installs
- .env.example: document DOCKER_BUILDKIT=1 for Colima users

ui-v2/src/app.css

@@ -0,0 +1,65 @@
+@import "tailwindcss";
+
+@theme {
+	--color-brand: #f59e0b;       /* amber-400 */
+	--color-brand-dim: #d97706;   /* amber-600 */
+	--color-surface: #18181b;     /* zinc-900 */
+	--color-surface-2: #27272a;   /* zinc-800 */
+	--color-surface-3: #3f3f46;   /* zinc-700 */
+	--color-muted: #a1a1aa;       /* zinc-400 */
+	--color-text: #f4f4f5;        /* zinc-100 */
+}
+
+html {
+	background-color: var(--color-surface);
+	color: var(--color-text);
+}
+
+/* ── Chapter prose ─────────────────────────────────────────────────── */
+.prose-chapter {
+	max-width: 72ch;
+	line-height: 1.85;
+	font-size: 1.05rem;
+	color: #d4d4d8; /* zinc-300 */
+}
+
+.prose-chapter h1,
+.prose-chapter h2,
+.prose-chapter h3 {
+	color: #f4f4f5;
+	font-weight: 700;
+	margin-top: 1.5em;
+	margin-bottom: 0.5em;
+}
+
+.prose-chapter h1 { font-size: 1.4rem; }
+.prose-chapter h2 { font-size: 1.2rem; }
+.prose-chapter h3 { font-size: 1.05rem; }
+
+.prose-chapter p {
+	margin-bottom: 1.2em;
+}
+
+.prose-chapter em {
+	color: #a1a1aa;
+}
+
+.prose-chapter strong {
+	color: #f4f4f5;
+}
+
+.prose-chapter hr {
+	border-color: #3f3f46;
+	margin: 2em 0;
+}
+
+/* ── Navigation progress bar ───────────────────────────────────────── */
+@keyframes progress-bar {
+	0%   { width: 0%; opacity: 1; }
+	80%  { width: 90%; opacity: 1; }
+	100% { width: 100%; opacity: 0; }
+}
+.animate-progress-bar {
+	animation: progress-bar 8s cubic-bezier(0.1, 0.05, 0.1, 1) forwards;
+}
+