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/fuzz/fuzz_bencode.c

@@ -0,0 +1,11 @@
+#include "naut/bencode.h"
+/* libFuzzer entry: parse arbitrary bytes; ASan/UBSan catch any memory or UB. */
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+    naut_bc_doc *d = NULL;
+    if (naut_bc_parse(data, size, &d) == NAUT_OK) {
+        const naut_bc *r = naut_bc_root(d);
+        (void)naut_bc_dict_get(r, "info");   /* exercise accessors */
+        naut_bc_free(d);
+    }
+    return 0;
+}