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/lib/house-tracker/ListingMap.svelte

@@ -72,18 +72,17 @@
 		(async () => {
 			try {
 				const { Map, Popup, config, LngLatBounds } = await import('@maptiler/sdk');
-				const { env } = await import('$env/dynamic/public');
+				const { PUBLIC_MAPTILER_API_KEY } = await import('$app/env/public');
 				if (destroyed) return;
-				if (!env.PUBLIC_MAPTILER_API_KEY) {
+				if (!PUBLIC_MAPTILER_API_KEY) {
 					mapError = 'Map needs PUBLIC_MAPTILER_API_KEY.';
 					return;
 				}
-				config.apiKey = env.PUBLIC_MAPTILER_API_KEY;
+				config.apiKey = PUBLIC_MAPTILER_API_KEY;
 				map = new Map({
 					container,
 					style:
-						'https://api.maptiler.com/maps/streets-v2/style.json?key=' +
-						env.PUBLIC_MAPTILER_API_KEY,
+						'https://api.maptiler.com/maps/streets-v2/style.json?key=' + PUBLIC_MAPTILER_API_KEY,
 					center: [4.7104, 52.0115],
 					zoom: 11,
 					cooperativeGestures: true

src/lib/house-tracker/types.ts

@@ -1,5 +1,5 @@
 // Shared between the home worker (scripts/house-worker.ts), the ingest API and
-// the page. Keep this file free of `$lib` / `$env` imports: the worker runs it
+// the page. Keep this file free of `#lib` / `$app/env` imports: the worker runs it
 // directly with bun, outside SvelteKit.
 import { z } from 'zod';