feat(mvp): phase 1 - project scaffolding & tooling

Initialize SvelteKit project with Svelte 5, TypeScript strict, Tailwind CSS v4,
shadcn-svelte, Prisma + SQLite, Vitest, ESLint, Prettier. Add Docker multi-stage
build, docker-compose, and Gitea Actions CI pipeline.

src/app.d.ts

@@ -0,0 +1,31 @@
+// See https://svelte.dev/docs/kit/types#app.d.ts
+
+declare global {
+	namespace App {
+		interface Error {
+			message: string;
+			code?: string;
+		}
+
+		interface Locals {
+			user: {
+				id: string;
+				username: string;
+				role: 'admin' | 'user' | 'guest';
+			} | null;
+			session: {
+				id: string;
+				expiresAt: Date;
+			} | null;
+		}
+
+		interface PageData {
+			user: App.Locals['user'];
+		}
+
+		// interface PageState {}
+		// interface Platform {}
+	}
+}
+
+export {};