feat: upgrade to SvelteKit 3 and adapter-bun

Run the sveltekit-3 migration and finish its manual tasks:

- Move kit config into the sveltekit() Vite plugin; drop svelte.config.js
- Replace $lib with #lib subpath imports
- Declare env vars in src/env.ts and import them from $app/env/{private,public}
- Consolidate param matchers into src/params.ts
- Use error(status, message), Response.json, refreshAll and goto reset/shallow
- Fall back to a full page load when goto rejects a login return path

Switch from adapter-node to adapter-bun: the build script runs Vite under
Bun (the adapter requires it) and the image starts with `bun ./build`.
Runtime env names (PORT, BODY_SIZE_LIMIT, ADDRESS_HEADER, ...) are unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/routes/projects/progress/create/+page.server.ts

@@ -1,7 +1,7 @@
-import { requireAdmin } from '$lib/server/authorization';
+import { requireAdmin } from '#lib/server/authorization.js';
 import type { Actions } from './$types';
-import { db } from '$lib/server/db';
-import { tasks } from '$lib/server/db/schema';
+import { db } from '#lib/server/db/index.js';
+import { tasks } from '#lib/server/db/schema/index.js';
 import { redirect } from '@sveltejs/kit';
 
 export const actions: Actions = {

src/routes/projects/progress/create/+page.svelte

@@ -1,13 +1,13 @@
 <script lang="ts">
 	import { resolve } from '$app/paths';
-	import { Button } from '$lib/components/ui/button/index.js';
-	import { Input } from '$lib/components/ui/input/index.js';
-	import { Label } from '$lib/components/ui/label/index.js';
-	import * as Card from '$lib/components/ui/card/index.js';
+	import { Button } from '#lib/components/ui/button/index.js';
+	import { Input } from '#lib/components/ui/input/index.js';
+	import { Label } from '#lib/components/ui/label/index.js';
+	import * as Card from '#lib/components/ui/card/index.js';
 </script>
 
 <div class="mx-auto max-w-xl space-y-6 px-4 py-12 sm:px-6">
-	<Button href={resolve('/projects/progress')} variant="ghost" size="sm">← All tasks</Button>
+	<Button href={resolve('projects/progress')} variant="ghost" size="sm">← All tasks</Button>
 	<Card.Root
 		><Card.Header><Card.Title>Create task</Card.Title></Card.Header><Card.Content
 			><form method="POST" class="space-y-4">