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/+page.svelte

@@ -2,10 +2,10 @@
 	import { resolve } from '$app/paths';
 	import ArrowRight from 'lucide-svelte/icons/arrow-right';
 	import ExternalLink from 'lucide-svelte/icons/external-link';
-	import * as Card from '$lib/components/ui/card/index.js';
-	import { Badge } from '$lib/components/ui/badge/index.js';
-	import ProjectIcon from '$lib/components/ProjectIcon.svelte';
-	import { projects } from '$lib/projects';
+	import * as Card from '#lib/components/ui/card/index.js';
+	import { Badge } from '#lib/components/ui/badge/index.js';
+	import ProjectIcon from '#lib/components/ProjectIcon.svelte';
+	import { projects } from '#lib/projects.js';
 
 	const earlier = [
 		'distributor',