feat(stdlib): finish Crypto (CSPRNG + base64) and add Uuid.* library (#19 #16)

Crypto (#19): add the OS cryptographically-secure random surface
(random_bytes/random_hex/random_u32, reading /dev/urandom) and a standard
base64 encoder, completing the library alongside the existing SHA-256/
HMAC-SHA256/verify_hmac/hex/ct_equal. All pure integer IR, C-free.

Uuid (#16): a new namespace for stable, collision-free IDs — v4 (random) and
v7 (time-ordered) generation, plus parse/is_valid/to_text/equals/nil. UUIDs are
canonical lowercase 36-char strings; v4 and v7's random tail draw from the
crypto CSPRNG, so both carry the documented determinism caveat (mint at the
edges, never inside lockstep simulation). Reuses the crypto prelude's
fn_secure_bytes / fn_hex_encode.

- examples/library/{crypto,uuid}.ludic: known-answer vectors (SHA-256, HMAC,
  base64 per RFC 4231/4648) and structural invariants (uuid version/variant
  bits, parse/equals), wired into `x test` (now 51 passed).
- docs: per-symbol pages for every new method + a new Uuid section; inventory
  and impl-vs-docs coverage check pass.
- seed regenerated; `x bootstrap-cfree` fixpoint holds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/language/crypto/_section.md

@@ -8,4 +8,6 @@ Secure, test-vector-backed hashing for the handful of security-sensitive things
 
 Digests are returned as lowercase hex strings, not raw bytes — a <code>str</code> is null-terminated and a raw digest can contain a zero byte, so hex is the form you can print, store, and compare directly.
 
+Alongside hashing, this library exposes the OS cryptographically-secure random generator — <a href="crypto-random_bytes"><code>random_bytes</code></a>, <a href="crypto-random_hex"><code>random_hex</code></a>, and <a href="crypto-random_u32"><code>random_u32</code></a> — for tokens, nonces, and <a href="ns-Uuid"><code>Uuid</code></a> generation, plus <a href="crypto-base64"><code>base64</code></a> for moving bytes through text-only channels. The secure-random helpers are deliberately non-deterministic and must never seed the lockstep simulation RNG (<a href="ns-Random"><code>Random</code></a>).
+
 What this is not: it is not DRM and it is not unbeatable anti-cheat. A client-side game cannot keep a secret from the machine it runs on — a determined owner can always read the key out of the binary. Use it to make *casual* tampering detectable and to authenticate messages between parties who share a key. To verify a MAC always use <a href="crypto-verify_hmac"><code>Crypto.verify_hmac</code></a> (a constant-time check), never <code>==</code>, which leaks how much of a guessed MAC was correct.