docs: update project docs for weighted proxy selection

Add selection weight section to USAGE.md with decay formula and
reference table. Mark feature complete in ROADMAP and TASKS.
Update README and PROJECT descriptions.

README.md

@@ -11,7 +11,7 @@ through configurable chains of SOCKS4, SOCKS5, and HTTP CONNECT proxies.
 - Per-hop authentication (username/password)
 - DNS leak prevention (domain names forwarded to proxies, never resolved locally)
 - Tor integration (Tor is just another SOCKS5 hop)
-- Managed proxy pool: multiple sources (API + file), health-tested, auto-cleaned
+- Managed proxy pool: multiple sources (API + file), health-tested, weighted selection
 - Connection retry with proxy rotation (configurable attempts)
 - Connection metrics (logged periodically and on shutdown)
 - Container-ready (Alpine-based, podman/docker)
@@ -97,10 +97,11 @@ Options:
 ## How Chaining Works
 
 ```
-Client -> s5p -> [static chain] -> [random alive proxy from pool] -> Destination
+Client -> s5p -> [static chain] -> [weighted alive proxy from pool] -> Destination
 ```
 
 s5p connects to Hop1 via TCP, negotiates the hop protocol (SOCKS5/4/HTTP),
 then over that tunnel negotiates with Hop2, and so on. If a proxy pool is
-configured, a random health-tested proxy is appended to the chain per-connection.
-Each hop only sees its immediate neighbors.
+configured, an alive proxy is appended per-connection, weighted toward those
+with the most recent successful health test. Each hop only sees its immediate
+neighbors.