forum: image attachments on threads + replies, AVIF picture render

New ImageAttachButton drops onto any composer textarea: file picker
upload → /api/upload/image (the universal pipeline) → markdown
![alt](primaryUrl) appended to the body. New thread + reply composers
both gain the button with a 'Auto-optimized, never > 20 MB' caption.

RichBody is the read-path companion: parses body markdown for image
syntax and renders each as a <picture> element with the AVIF source
first (derived from the .webp sibling on our bb-media bucket), then the
WebP, then the original-format fallback img. Prose around images still
runs through LinkifyPlainText so company auto-links still work.

Forum users now have a way to include screenshots, gear photos, NAB
booth shots, etc. in their posts — every image flows through the same
optimization that gives <10% of original byte weight at visually
identical quality.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/forum/[slug]/page.tsx

@@ -4,6 +4,7 @@ import Link from 'next/link';
 import { useParams } from 'next/navigation';
 import Header from '@/components/Header';
 import Footer from '@/components/Footer';
+import ImageAttachButton from '@/components/forum/ImageAttachButton';
 import { createClient } from '@/lib/supabase/client';
 
 interface ForumCategory {
@@ -336,6 +337,10 @@ export default function ForumCategoryPage() {
                   rows={5}
                   className="w-full bg-[#111] border border-[#333] rounded-lg px-3 py-2 text-white font-body text-sm placeholder-[#555] focus:outline-none focus:border-[#3b82f6] resize-none"
                 />
+                <div className="flex items-center gap-3">
+                  <ImageAttachButton onInsert={(md) => setNewBody((b) => (b || "") + md)} />
+                  <span className="text-[10px] text-[#666]">Auto-optimized, never &gt; 20 MB</span>
+                </div>
                 {newError && (
                   <div className="bg-[#2a0a0a] border border-[#cc0000] text-[#ff8a8a] font-body text-sm px-3 py-2 rounded">
                     {newError}