Initial commit: Naut-Torrent — from-scratch 10 GbE BitTorrent client

A maintainable, extensible BitTorrent client (C11, Linux/io_uring) targeting
10 GbE saturation. All torrent functionality is built from scratch; liburing
is the only linked third-party dependency on the data path.

Implements Phases 1-7 of the roadmap:
- core: page-aligned buffer pool, MPMC/Treiber queues, bitfields, worker pool
- crypto: SHA-1/256 (SHA-NI + scalar), Merkle (BEP-52), RC4 (MSE)
- bencode/metainfo: zero-copy parser, v1/v2/hybrid .torrent + magnet
- peer: sans-IO wire codec, MSE/PE handshake state machine, BEP-10, ut_metadata, PEX
- piece/storage: block-level multi-peer engine, rarest-first + endgame,
  per-file completion events + single-file relocate (move-as-you-finish)
- tracker/dht: HTTP + UDP (BEP-15) trackers, BEP-5 KRPC iterative lookup
- platform: io_uring reactor (SQPOLL, registered buffers, SEND_ZC)
- surface: versioned RPC, native plugin ABI, sandboxed Lua scripting, nautd/nautctl

Verified against libtorrent (single/multi/hybrid, MSE, magnet-via-DHT, swarm);
unit + interop tests green; ASan/UBSan/TSan clean. Scripting reference in
docs/scripting.md.

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

tests/unit/test.h

@@ -0,0 +1,34 @@
+/* Minimal test harness: no dependencies, exit code = failure count. */
+#ifndef NAUT_TEST_H
+#define NAUT_TEST_H
+#include <stdio.h>
+#include <stdlib.h>
+
+static int naut_test_fails = 0;
+static int naut_test_count = 0;
+
+#define CHECK(cond) do { \
+    naut_test_count++; \
+    if (!(cond)) { \
+        naut_test_fails++; \
+        fprintf(stderr, "  FAIL %s:%d: %s\n", __FILE__, __LINE__, #cond); \
+    } \
+} while (0)
+
+#define CHECK_EQ(a, b) do { \
+    long long _a = (long long)(a), _b = (long long)(b); \
+    naut_test_count++; \
+    if (_a != _b) { \
+        naut_test_fails++; \
+        fprintf(stderr, "  FAIL %s:%d: %s (%lld) == %s (%lld)\n", \
+                __FILE__, __LINE__, #a, _a, #b, _b); \
+    } \
+} while (0)
+
+#define TEST_MAIN_END() do { \
+    fprintf(stderr, "%s: %d checks, %d failures\n", \
+            __FILE__, naut_test_count, naut_test_fails); \
+    return naut_test_fails ? 1 : 0; \
+} while (0)
+
+#endif