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/cs-prices/api/series/+server.ts

@@ -1,6 +1,5 @@
-import { db } from '$lib/server/db';
+import { db } from '#lib/server/db/index.js';
 import { sql } from 'drizzle-orm';
-import { json } from '@sveltejs/kit';
 import type { RequestHandler } from './$types';
 
 const maxSeries = 1000;
@@ -24,13 +23,13 @@ export const POST: RequestHandler = async ({ request }) => {
 		ids.some((id) => !Number.isSafeInteger(id) || id <= 0) ||
 		values.some((value) => typeof value !== 'string' || value.length > 200)
 	)
-		return json({ error: 'Invalid selection' }, { status: 400 });
+		return Response.json({ error: 'Invalid selection' }, { status: 400 });
 	if (dimension === 'item' ? !ids.length : !values.length)
-		return json({ series: [], bucketSeconds: 0 });
+		return Response.json({ series: [], bucketSeconds: 0 });
 	const to = new Date(typeof body.to === 'string' ? body.to : Date.now());
 	const from = new Date(typeof body.from === 'string' ? body.from : to.getTime() - 365 * 86400_000);
 	if (Number.isNaN(+from) || Number.isNaN(+to) || from >= to || +to - +from > maxDays * 86400_000)
-		return json({ error: 'Invalid date range' }, { status: 400 });
+		return Response.json({ error: 'Invalid date range' }, { status: 400 });
 	// Aim for at most 240 buckets per series. Raw observations remain untouched.
 	const seconds = Math.max(60, Math.ceil((+to - +from) / 1000 / 240 / 60) * 60);
 	const selection =
@@ -64,5 +63,5 @@ export const POST: RequestHandler = async ({ request }) => {
 			count(*)::int AS items, sum(volume)::bigint AS volume,
 			min(min_cents)::int AS min_cents, max(max_cents)::int AS max_cents
 		FROM per_item GROUP BY 1, 2 ORDER BY 1, 2`);
-	return json({ bucketSeconds: seconds, currency, source, kind, points: rows });
+	return Response.json({ bucketSeconds: seconds, currency, source, kind, points: rows });
 };