docs(tests): TEST_CASES.md + wire-tap proof for university practice

Adds proof artifacts that the PQ tunnel is real:

- crates/aura-proto/tests/pq_wire_tap.rs — new integration test that
  intercepts every byte flowing on the in-memory transport and asserts:
  (1) ClientHello payload = 32 + 1184 + 32 (X25519 + ML-KEM-768 ek + nonce),
  (2) ServerHello payload = 32 + 1088 + 32 (X25519_eph + ML-KEM-768 ct + nonce),
  (3) a 56-byte plaintext marker shipped in a Data frame is absent from
      the wire in both directions,
  (4) ServerAuth/Data AEAD bodies have Shannon entropy >= 7 bits/byte.

- TEST_CASES.md — Russian-language report mapping 12 test cases to the
  exact code and captured outputs (KAT, hybrid round-trip, AEAD tamper
  detection, mutual X.509 rejection, replay window, 1000-packet flow,
  in-vivo ping, bench-crypto timings, new wire-tap proof).

- docs/test_evidence/ — full captured stdout of cargo test runs and
  aura bench-crypto, referenced from TEST_CASES.md.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/test_evidence/pq_wire_tap.txt

@@ -0,0 +1,17 @@
+    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.11s
+     Running tests/pq_wire_tap.rs (target/debug/deps/pq_wire_tap-738259f6ef41df6b)
+
+running 2 tests
+test shannon_entropy_baseline ... ok
+=== Aura PQ wire-tap test summary ===
+client_peer = "vpn.aura.example", server_peer = "client-pq-proof"
+captured c->s = 2869 bytes, s->c = 1723 bytes
+ClientHello payload = 1248 bytes (= 32 + 1184 + 32, X25519 + ML-KEM-768 ek + nonce)
+ServerHello payload = 1152 bytes (= 32 + 1088 + 32, X25519_eph + ML-KEM-768 ct + nonce)
+ServerAuth body Shannon entropy = 7.580 bits/byte over 474 bytes
+Data record AEAD body Shannon entropy = 7.829 bits/byte over 1101 bytes (plaintext was marker + 1024 zero bytes; zeros become keystream after ChaCha20)
+Plaintext marker present on wire? c->s: NO, s->c: NO
+test pq_handshake_and_data_wire_capture ... ok
+
+test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.02s
+