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/forum/ReplyForm.jsx

@@ -0,0 +1,82 @@
+import React, { useState, useRef, useCallback } from 'react'
+import Button from '../ui/Button'
+import RichTextEditor from './RichTextEditor'
+
+export default function ReplyForm({ threadId, prefill = '', quotedAuthor = null, csrfToken }) {
+  const [content, setContent] = useState(prefill)
+  const [submitting, setSubmitting] = useState(false)
+  const [error, setError] = useState(null)
+  const formRef = useRef(null)
+
+  const handleSubmit = useCallback(async (e) => {
+    e.preventDefault()
+    if (submitting || content.trim().length < 2) return
+
+    setSubmitting(true)
+    setError(null)
+
+    try {
+      const res = await fetch(`/forum/thread/${threadId}/reply`, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          'X-CSRF-TOKEN': csrfToken,
+          'Accept': 'application/json',
+          'X-Requested-With': 'XMLHttpRequest',
+        },
+        credentials: 'same-origin',
+        body: JSON.stringify({ content: content.trim() }),
+      })
+
+      if (res.ok) {
+        // Reload page to show new reply
+        window.location.reload()
+      } else if (res.status === 422) {
+        const json = await res.json()
+        setError(json.errors?.content?.[0] ?? 'Validation error.')
+      } else {
+        setError('Failed to post reply. Please try again.')
+      }
+    } catch {
+      setError('Network error. Please try again.')
+    }
+
+    setSubmitting(false)
+  }, [content, threadId, csrfToken, submitting])
+
+  return (
+    <form
+      ref={formRef}
+      onSubmit={handleSubmit}
+      className="space-y-4 rounded-2xl border border-white/[0.06] bg-nova-800/50 p-5 backdrop-blur"
+    >
+      {quotedAuthor && (
+        <p className="text-xs text-cyan-400/70">
+          Replying with quote from <strong className="text-cyan-300">{quotedAuthor}</strong>
+        </p>
+      )}
+
+      {/* Rich text editor */}
+      <RichTextEditor
+        content={content}
+        onChange={setContent}
+        placeholder="Write your reply…"
+        error={error}
+        minHeight={10}
+      />
+
+      {/* Submit */}
+      <div className="flex items-center justify-end">
+        <Button
+          type="submit"
+          variant="primary"
+          size="md"
+          loading={submitting}
+          disabled={content.trim().length < 2}
+        >
+          Post reply
+        </Button>
+      </div>
+    </form>
+  )
+}