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_pipeline.c

@@ -0,0 +1,30 @@
+#include "naut/pipeline.h"
+#include "test.h"
+
+int main(void) {
+    naut_pipeline pipeline;
+    naut_pipeline_init(&pipeline, NAUT_BLOCK, 4, 1024, 32);
+    CHECK_EQ(naut_pipeline_depth(&pipeline), 32);
+
+    /* 16 KiB every 100 us with 20 ms RTT is about 164 MB/s and a 200-block
+     * BDP. Repeated samples should grow the window substantially. */
+    double now = 1.0;
+    for (int i = 0; i < 100; i++) {
+        now += 0.0001;
+        naut_pipeline_on_block(&pipeline, NAUT_BLOCK, now - 0.020, now);
+    }
+    CHECK(naut_pipeline_depth(&pipeline) > 128);
+    CHECK(naut_pipeline_depth(&pipeline) <= 1024);
+
+    uint32_t high = naut_pipeline_depth(&pipeline);
+    for (int i = 0; i < 100; i++) {
+        now += 0.050;
+        naut_pipeline_on_block(&pipeline, NAUT_BLOCK, now - 0.005, now);
+    }
+    CHECK(naut_pipeline_depth(&pipeline) < high);
+    CHECK(naut_pipeline_depth(&pipeline) >= 4);
+
+    naut_pipeline_init(&pipeline, 0, 0, 0, 0);
+    CHECK_EQ(naut_pipeline_depth(&pipeline), 1);
+    TEST_MAIN_END();
+}