refactor: clap CLI parser, safety docs, dead code docs, cross-refs

Audit items 6, 8, 9, 10:

#6 - Relay CLI: replaced 154-line manual parse_args() with clap derive
     (13 flags/options preserved, auto --help, --version from build hash)
#8 - wzp-native: added # Safety docs to all 3 unsafe extern "C" fns
#9 - wzp-crypto: documented x25519_static_secret/public as reserved for
     future static-key federation auth (not dead code, intentionally unused)
#10 - Cross-references between quality.rs ↔ dred_tuner.rs module docs

368 tests passing, 0 regressions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-crypto/src/handshake.rs

@@ -18,10 +18,14 @@ use crate::session::ChaChaSession;
 pub struct WarzoneKeyExchange {
     /// Ed25519 signing key (identity).
     signing_key: SigningKey,
-    /// X25519 static secret (derived from seed, used for identity encryption).
+    /// X25519 static secret derived from identity seed. Reserved for future
+    /// use in static-key federation authentication (not used in current
+    /// ephemeral-only handshake protocol).
     #[allow(dead_code)]
     x25519_static_secret: StaticSecret,
-    /// X25519 static public key.
+    /// X25519 static public key derived from identity seed. Reserved for
+    /// future use in static-key federation authentication (not used in
+    /// current ephemeral-only handshake protocol).
     #[allow(dead_code)]
     x25519_static_public: X25519PublicKey,
     /// Ephemeral X25519 secret for the current call (set by generate_ephemeral).