feat: configurable upload file size limits via .env (#695)

* feat: make upload file size limits configurable via .env

Add UPLOAD_MAX_*_MB environment variables for documents, images, videos,
exercise assignment files, AI assistant documents, landing page images,
and media thumbnails. API presign routes validate file size server-side;
dashboard UI reads the same limits from layout data.

* chore: wire upload limit env vars through Docker compose and docs

Pass UPLOAD_MAX_*_MB from the root .env into api and dashboard containers
in both compose files, document them in .env.example and self-hosting guides.

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* docs: cross-link upload limits in README, Railway, Coolify, and Cloudflare guides

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix: address PR review feedback on upload limits

- Restore 5 MB default for thumbnail uploads (edit-asset-dialog regression)
- Add getResolvedUploadLimits() fallback for Storybook/tests
- Cache core getUploadLimits() like the dashboard helper
- Document presign fileSize as advisory; allow zero-byte fileSize in schema
- Only send fileSize to presign when greater than zero

* docs: remove upload limits from Cloudflare setup guide

---------

apps/dashboard/src/routes/+layout.server.ts

@@ -1,8 +1,10 @@
 import type { AccountOrg } from '$features/app/types';
 import type { MetaTagsProps } from 'svelte-meta-tags';
+import type { UploadLimits } from '$lib/utils/config/upload-limits';
 import { PUBLIC_IS_SELFHOSTED } from '$env/static/public';
 import { getBaseMetaTags } from '$lib/utils/functions/metaTags';
 import { getOrgSiteInfo } from '$features/app/layout-setup';
+import { getUploadLimits } from '$lib/utils/config/upload-limits';
 
 export const ssr = true;
 
@@ -15,6 +17,7 @@ interface LoadOutput {
   serverLang: string;
   localeCookie: string;
   locals: App.Locals;
+  uploadLimits: UploadLimits;
 }
 
 export const load = async ({ url, cookies, request, locals }): Promise<LoadOutput> => {
@@ -33,7 +36,8 @@ export const load = async ({ url, cookies, request, locals }): Promise<LoadOutpu
     baseMetaTags: getBaseMetaTags(url, orgSiteInfo),
     serverLang: request.headers?.get('accept-language') || '',
     localeCookie: cookies.get('classroomio_locale') || '',
-    locals
+    locals,
+    uploadLimits: getUploadLimits()
   };
 
   const loadMs = Math.round((performance.now() - loadStart) * 100) / 100;

apps/dashboard/src/routes/+layout.svelte

@@ -16,8 +16,12 @@
 
   import '../app.css';
 
+  import { setUploadLimitsContext } from '$lib/utils/config/upload-limits-context';
+
   let { data, children } = $props();
 
+  setUploadLimitsContext(data.uploadLimits);
+
   const metaTags = $derived(merge(data.baseMetaTags, page.data.pageMetaTags));
 
   onMount(() => {