fix(build): disable prerender crawl so build stops OOMing

`/hikes` is `prerender = true` and carries the global nav, so the
prerender crawler followed those links and tried to statically render
the whole dynamic, DB-/ML-backed app. SvelteKit prerenders inside a
heap-capped worker_threads worker, so this exhausted its heap
(ERR_WORKER_OUT_OF_MEMORY) and failed the build.

- svelte.config.js: prerender.crawl = false. The intended static set is
  fully described by `prerender = true` (/hikes) + the /errors/[status]
  EntryGenerator, so crawling is unneeded. Add a defensive
  handleHttpError that ignores /hikes/*/images/* 404s (those binaries
  live in hikes-assets/, served by nginx/dev-middleware, not /static).
- hooks.server.ts: skip init when `building` so builds don't connect to
  Mongo, start the payment scheduler, or warm the romcal cache.
- hikes/[slug]: set `prerender = false`, enforcing the intent its
  comment already stated.

Version 1.86.1 -> 1.86.2.

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.86.1",
+	"version": "1.86.2",
 	"private": true,
 	"type": "module",
 	"scripts": {