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>

prisma/schema.prisma

@@ -46,6 +46,7 @@ model User {
   closedQuestions      StudentQuestion[]       @relation("QuestionClosedBy")
   questionMessages     StudentQuestionMessage[]
   wrappedRuns          WrappedRun[]
+  toolUsages           ToolUsage[]
 }
 
 // Obsidian Wrapped — агрегаты прогона (БЕЗ имён/текстов заметок; обработка волта 100% client-side)
@@ -68,6 +69,19 @@ model WrappedRun {
   @@index([userId])
 }
 
+// Obsidian Toolbox — факт использования генератора участником (для аналитики)
+model ToolUsage {
+  id        String   @id @default(cuid())
+  userId    String
+  user      User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+  tool      String // callout | frontmatter | theme | style-settings
+  createdAt DateTime @default(now())
+
+  @@index([userId])
+  @@index([tool])
+  @@index([createdAt])
+}
+
 model Session {
   id             String   @id @default(cuid())
   userId         String