Add Obsidian Toolbox — 4 syntax generators under /tools

Inside-LMS toolbox for registered students: callout-CSS, YAML-frontmatter,
theme CSS-variables, Style Settings generators. Auth inherited from (student)
route group; no public surface, no email gate.

- Pure generators in src/lib/tools/* with Vitest (33 tests)
- Shared YAML-safe scalar quoter (_shared/yaml.ts) used by frontmatter +
  style-settings: unquoted user input was silently breaking YAML (tags '#x'
  -> null, color default '#7C3AED' -> null, 'a: b' -> parse error)
- hex validation in callout (no NaN), date input constrained, clipboard +
  analytics calls guarded
- Prisma ToolUsage model + migration; logToolUsage Server Action (auth-first,
  10-min dedup window per user/tool)
- Tool index /tools + ToolCard (explicit lucide map, no import *) + header link

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -7,7 +7,8 @@
     "build": "next build",
     "start": "next start",
     "lint": "eslint",
-    "type-check": "tsc --noEmit"
+    "type-check": "tsc --noEmit",
+    "test": "vitest run"
   },
   "prisma": {
     "seed": "ts-node --project tsconfig.json prisma/seed.ts"
@@ -63,6 +64,7 @@
     "prisma": "^7.6.0",
     "tailwindcss": "^4",
     "ts-node": "^10.9.2",
-    "typescript": "^5"
+    "typescript": "^5",
+    "vitest": "^4.1.9"
   }
 }