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>

src/lib/tools/_shared/syntax-versions.json

@@ -0,0 +1,10 @@
+{
+  "checkedAt": "20260623",
+  "callout": { "ref": "Obsidian callouts (core)", "version": "obsidian-1.x" },
+  "frontmatter": { "ref": "Obsidian Properties (core)", "version": "obsidian-1.x" },
+  "styleSettings": {
+    "ref": "obsidian-community/obsidian-style-settings",
+    "version": "1.x",
+    "types": ["heading", "class-toggle", "class-select", "variable-text", "variable-number", "variable-number-slider", "variable-select", "variable-color", "info-text"]
+  }
+}