feat: forum rich-text editor, emoji picker, mentions, discover nav, feed, uploads, profile

Forum:
- TipTap WYSIWYG editor with full toolbar
- @emoji-mart/react emoji picker (consistent with tweets)
- @mention autocomplete with user search API
- Fix PHP 8.4 parse errors in Blade templates
- Fix thread data display (paginator items)
- Align forum page widths to max-w-5xl

Discover:
- Extract shared _nav.blade.php partial
- Add missing nav links to for-you page
- Add Following link for authenticated users

Feed/Posts:
- Post model, controllers, policies, migrations
- Feed page components (PostComposer, FeedCard, etc)
- Post reactions, comments, saves, reports, sharing
- Scheduled publishing support
- Link preview controller

Profile:
- Profile page components (ProfileHero, ProfileTabs)
- Profile API controller

Uploads:
- Upload wizard enhancements
- Scheduled publish picker
- Studio status bar and readiness checklist

resources/js/components/upload/ReadinessChecklist.jsx

@@ -0,0 +1,55 @@
+import React from 'react'
+
+/**
+ * ReadinessChecklist
+ *
+ * Shows upload readiness requirements with status icons.
+ * Each item can have an optional `href` to jump to the section for a quick fix.
+ */
+export default function ReadinessChecklist({ items = [] }) {
+  const allOk = items.every((item) => item.ok)
+
+  return (
+    <div>
+      <p className="mb-2 text-[10px] uppercase tracking-wider text-white/40">
+        Readiness
+      </p>
+      <ul className="space-y-1" role="list">
+        {items.map((item) => (
+          <li key={item.label} className="flex items-center gap-2 text-xs">
+            <span
+              className={[
+                'flex h-4 w-4 shrink-0 items-center justify-center rounded-full text-[9px] font-bold',
+                item.ok
+                  ? 'bg-emerald-500/25 text-emerald-300'
+                  : 'bg-white/8 text-white/30',
+              ].join(' ')}
+              aria-hidden="true"
+            >
+              {item.ok ? '✓' : '○'}
+            </span>
+            <span className={item.ok ? 'text-white/70' : 'text-white/40'}>
+              {(item.onClick || item.href) && !item.ok ? (
+                <button
+                  type="button"
+                  onClick={item.onClick}
+                  className="text-sky-400 hover:underline focus-visible:outline-none focus-visible:underline"
+                >
+                  {item.label}
+                </button>
+              ) : (
+                item.label
+              )}
+            </span>
+            {item.optional && !item.ok && (
+              <span className="ml-auto text-[9px] text-white/25 italic">optional</span>
+            )}
+          </li>
+        ))}
+      </ul>
+      {allOk && (
+        <p className="mt-2 text-[11px] text-emerald-300/80">All requirements met.</p>
+      )}
+    </div>
+  )
+}