docs: document control API

Add API section to README (features, CLI, config), PROJECT (architecture),
USAGE (full endpoint reference with examples), CHEATSHEET (curl one-liners).
Update TASKS and ROADMAP.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

PROJECT.md

@@ -25,6 +25,7 @@ Client -------> s5p -------> Hop 1 -------> Hop 2 -------> Target
 - **pool.py** -- managed proxy pool (multi-source, health-tested, persistent)
 - **http.py** -- minimal async HTTP/1.1 client (GET/POST JSON, no external deps)
 - **connpool.py** -- pre-warmed TCP connection pool to first chain hop
+- **api.py** -- built-in HTTP control API (runtime metrics, pool state, config reload)
 - **cli.py** -- argparse CLI, logging setup, cProfile support
 - **metrics.py** -- connection counters and human-readable summary (lock-free, asyncio-only)
 
@@ -66,3 +67,4 @@ All other functionality uses Python stdlib (`asyncio`, `socket`, `struct`).
 - **Connection semaphore** -- cap concurrent connections to prevent fd exhaustion
 - **Async HTTP** -- native asyncio HTTP client replaces blocking urllib, parallel fetches
 - **First-hop pool** -- pre-warmed TCP connections to chain[0], stale-evicted, auto-refilled
+- **Control API** -- built-in asyncio HTTP server, no Flask/external deps, disabled by default