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/components/tools/CodeOutput.tsx

@@ -0,0 +1,21 @@
+import { CopyButton } from "./CopyButton";
+import type { ToolId } from "@/lib/tools/_shared/types";
+
+export function CodeOutput({ code, tool, label }: { code: string; tool: ToolId; label?: string }) {
+  return (
+    <div className="flex flex-col gap-2">
+      {label && <div className="text-xs font-bold tracking-wide" style={{ color: "var(--muted-foreground)" }}>{label}</div>}
+      <pre
+        className="overflow-auto p-3 text-sm"
+        style={{
+          fontFamily: "var(--font-mono, 'Fira Mono', monospace)",
+          border: "1px solid var(--border)",
+          borderRadius: "2px",
+          backgroundColor: "var(--background)",
+          color: "var(--foreground)",
+        }}
+      >{code}</pre>
+      <div><CopyButton text={code} tool={tool} /></div>
+    </div>
+  );
+}