Replace the custom Alpine.js textarea + mention system with Filament v5's
built-in RichEditor component and MentionProvider. This fixes Alpine scope
errors (showMentions/mentionResults not defined) that occurred during
Livewire DOM morphing inside Filament slide-over modals.
- Add InteractsWithForms + HasForms to Comments and CommentItem components
- Define commentForm(), editForm(), replyForm() with RichEditor + mentions
- Add CommentsConfig::makeMentionProvider() shared helper
- Update MentionParser to extract mention IDs from RichEditor HTML format
- Update Comment::renderBodyWithMentions() to use RichContentRenderer
- Remove all custom Alpine.js mention code from blade templates
- Backward compatible with existing plain text comments
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