feat: complete UI redesign — editorial-paper palette, Monaco theme, lucide icons, primitives

Palette overhaul:
- Warm cream canvas (#faf8f4) + near-white surfaces (#fdfdfb) + deep teal accent (#0f766e)
- Unified on stone-warm neutrals via @theme block in index.css

Typography:
- Inter Variable + JetBrains Mono Variable via fontsource (self-hosted)
- Monaco editor set to JetBrains Mono for consistency

Icons:
- lucide-react replaces all 8 hand-rolled SVGs
- Leaf brand mark beside wordmark

Shared primitives (src/components/ui/):
- Icon, Button (4 variants, 2 sizes), IconButton, TextInput, SectionHeader, StatusDot, Chip

Custom Monaco theme (src/theme/monaco-theme.ts):
- typst-leaf-light: warm near-white background, restrained rainbow-free syntax
- Keywords teal, strings warm green, comments stone italic, most tokens ink

Component reworks:
- TopBar: Leaf icon, h-12, chip-based status, Button/IconButton primitives
- Sidebar: w-72, icon+label tabs with teal bottom border
- StatusBar: lucide GitBranch/ArrowUp/ArrowDown, chip-based status
- FileTree: lucide Plus/FolderPlus/Pencil/Trash2, teal active state
- GitPanel: lucide status icons, restored staged/unstaged bg tint
- Preview: RotateCw reload icon, chip status
- EmptyState: muted Leaf icon
- ToastHost: StatusDot + lucide X

Fixes:
- GitPanel staged/unstaged/untracked rows now have distinct bg tints
- Button defaults to type="button" to prevent accidental form submission
- Editor error fallback from red-400 to rose-600
- DESIGN.md: removed emoji from layout skeleton, fixed Modals/Monaco typo

Build: pnpm -r typecheck + pnpm build pass.

typst-leaf-frontend/package.json

@@ -11,9 +11,12 @@
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
+    "@fontsource-variable/inter": "^5.2.8",
+    "@fontsource-variable/jetbrains-mono": "^5.2.8",
     "@monaco-editor/react": "^4.7.0",
     "@tauri-apps/api": "^2",
     "@tauri-apps/plugin-opener": "^2",
+    "lucide-react": "^1.23.0",
     "monaco-editor": "^0.55.1",
     "monaco-vim": "^0.4.4",
     "react": "^19.1.0",
@@ -22,13 +25,13 @@
   },
   "devDependencies": {
     "@tailwindcss/vite": "^4.1.6",
+    "@tauri-apps/cli": "^2",
     "@types/react": "^19.1.8",
     "@types/react-dom": "^19.1.6",
     "@vitejs/plugin-react": "^4.6.0",
     "tailwindcss": "^4.1.6",
     "typescript": "~5.8.3",
-    "vite": "^7.0.4",
-    "@tauri-apps/cli": "^2"
+    "vite": "^7.0.4"
   },
   "packageManager": "pnpm@10.23.0"
 }