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/uuid/uuid-equals.md

@@ -0,0 +1,27 @@
+---
+id: uuid-equals
+name: Uuid.equals
+category: uuid
+kind: namespace-method
+tokens: Uuid.equals
+sig: Uuid.equals(a, b) -> bool
+tip: Case-insensitive UUID equality.
+order: 8
+ns: Uuid
+member: equals
+---
+
+Compares two UUIDs for equality, ignoring case. UUIDs generated by this library are always lowercase, so a plain <code>==</code> works between them — but a UUID that arrived from another system may be upper- or mixed-case, and <code>equals</code> matches it correctly without you having to normalise first. Values of different length are never equal.
+
+Parameters:
+- `a`, `b` — the UUID strings to compare
+
+```ludic
+program Eq {
+  entry {
+    let lo = "550e8400-e29b-41d4-a716-446655440000"
+    let up = "550E8400-E29B-41D4-A716-446655440000"
+    if Uuid.equals(lo, up) { print(1) }   # case-insensitive
+  }
+}
+```