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.

src/hooks.server.ts

@@ -1,6 +1,7 @@
 import type { Handle, HandleServerError, ServerInit } from "@sveltejs/kit"
 import { redirect } from "@sveltejs/kit"
 import { sequence } from "@sveltejs/kit/hooks"
+import { building } from "$app/environment"
 import * as auth from "./auth"
 import { initializeScheduler } from "./lib/server/scheduler"
 import { dbConnect } from "./utils/db"
@@ -122,6 +123,15 @@ async function timing({ event, resolve }: Parameters<Handle>[0]) {
 }
 
 export const init: ServerInit = async () => {
+  // SvelteKit runs prerendering/analysis inside a worker_threads worker (see
+  // @sveltejs/kit utils/fork.js) whose JS heap is capped well below the main
+  // thread's. `init` fires there too, so warming the romcal cache during a
+  // build exhausts that worker's heap → ERR_WORKER_OUT_OF_MEMORY and a failed
+  // build. None of it is needed at build time: no prerendered route touches the
+  // DB, and connecting to Mongo / starting the payment scheduler from a build
+  // is undesirable regardless. Skip startup work while building.
+  if (building) return;
+
   console.log('🚀 Server starting - initializing database connection...');
   try {
     await dbConnect();