Enable Next.js image optimization across ~60 remaining unoptimized <Image> spots

- Remove `unoptimized` from every Image that was pointing at a real remote/
  static file (Reels image carousel, story avatars/viewer, shop product
  grids/details, chat shared-post/product/story bubbles, notification/
  visitor rows, tag/mention pickers, etc.) so Next's own resize+avif/webp
  pipeline (already configured in next.config.ts) actually applies —
  previously only a handful of components used it, everything else shipped
  full-resolution originals regardless of the tiny thumbnail size shown
- Add a `sizes` prop wherever `fill` was used without one, so the optimizer
  picks an appropriately small srcset entry instead of defaulting to 100vw
- Fix ProfileAvatar to request the actual displayed size instead of always
  requesting 280x280 regardless of the `size` prop
- Left `unoptimized` on the handful of genuinely local/ephemeral sources
  (blob:/data: URIs from in-progress uploads, third-party QR API images,
  static SVG icons) where Next's optimizer can't or shouldn't apply
- Add next-story prefetch to StoryViewer (previously only Reels prefetched
  upcoming media; swiping to the next story always cold-started before)
- Fix .claude/launch.json's dev server port (3000 -> 3004) to match
  package.json's actual `next dev --port 3004`

Verified via `tsc --noEmit` (no new errors) and by diffing this app's
console/network behavior against a git-stashed baseline in the browser
preview — the one pre-existing hydration warning and 401s (unauthenticated
session) are present on both, and /_next/image requests now succeed for
avatars/thumbnails that previously bypassed optimization entirely.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.claude/launch.json

@@ -5,7 +5,7 @@
       "name": "modstagram-next-dev",
       "runtimeExecutable": "npm",
       "runtimeArgs": ["run", "dev"],
-      "port": 3000
+      "port": 3004
     }
   ]
 }