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>

selfhost/emit_core.ludic

@@ -26,6 +26,7 @@ var g_uses_textrt: bool = false  # Text.upper/lower/trim/repeat/pad was emitted
 var g_uses_textrt2: bool = false  # Text.split/join/replace was emitted -> emit the string/slice builders
 var g_uses_hashrt: bool = false  # Hash.of/fnv1a/crc32 was emitted -> emit the byte-stream hashers
 var g_uses_cryptort: bool = false  # Crypto.* was emitted -> emit the SHA-256 / HMAC runtime
+var g_uses_uuidrt: bool = false  # Uuid.* was emitted -> emit the UUID runtime (needs the crypto CSPRNG)
 var g_uses_datert: bool = false  # Date.*/DateTime.* was emitted -> emit the civil<->epoch conversions
 var g_uses_longstr: bool = false  # string(long) / interpolating a long was emitted -> emit fn_long_str