feat(ui): editor UX improvements — lowlight, upload, emoji, comment editing

- New QuickEmojiPicker: shared SmilePlus + 8 quick emojis + full picker
- New FileUploadButton: reusable Paperclip upload trigger
- New CodeBlockView: React NodeView with language label + copy button
- CodeBlockLowlight: syntax highlighting in editor (replaces plain codeBlock)
- ReactionBar: brand-tinted pill styles, hideAddButton prop
- Comment header: emoji picker + three-dot menu in top-right
- Comment edit: inline editing with brand border, blur-to-save, Escape-to-cancel
- RichTextEditor: add onBlur prop, markdown paste extension
- Create issue: upload button in footer
- Issue detail: upload button next to reaction bar
- Comment/reply: use FileUploadButton, loading spinners, no optimistic updates

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/package.json

@@ -18,6 +18,7 @@
     "@dnd-kit/utilities": "^3.2.2",
     "@emoji-mart/data": "^1.2.1",
     "@floating-ui/dom": "^1.7.6",
+    "@tiptap/extension-code-block-lowlight": "3.20.5",
     "@tiptap/extension-image": "^3.20.5",
     "@tiptap/extension-link": "^3.20.5",
     "@tiptap/extension-mention": "^3.20.5",
@@ -36,6 +37,7 @@
     "emoji-mart": "^5.6.0",
     "input-otp": "^1.4.2",
     "linkify-it": "^5.0.0",
+    "lowlight": "^3.3.0",
     "lucide-react": "catalog:",
     "next": "^16.1.6",
     "next-themes": "^0.4.6",