docs+plugin: HTTP-only transport cleanup, install guide, review fixes

- docs/install.md: new end-to-end guide for non-technical users
  (gateway install, app install, LAN/TLS/remote connection, push,
  options, troubleshooting); docs/setup.md now points to it
- README: new 'Install the gateway' section; pairing section updated
  for HTTP transport (8791, QR scan on Android)
- rename IRIS_WS_HOST -> IRIS_HTTP_HOST (clean rename, no compat
  fallback); drop dead DEFAULT_PORT=8790
- setup.py: advertise https:// in the printed/QR server URL when
  IRIS_HTTP_CERT is set
- ws_probe.py/e2e.py: default --url http://127.0.0.1:8791, env
  IRIS_WS_URL -> IRIS_HTTP_URL, honor explicit port + https scheme
- plugin.yaml: IRIS_HTTP_* env names, description no longer says
  'WebSocket server'
- docs 03/09/12/19: fix stale WS-era refs (ws_server.py cites,
  8790 smoke test, WSS->HTTPS, 'HTTP fallback' reframed as the
  only transport)
- AGENTS.md: symlink name android -> iris (matches actual install)
- test: adapter reads IRIS_HTTP_HOST/CERT/KEY from env; legacy
  IRIS_WS_* names are not consulted (95/95 pass)

gateway-plugin/tests/ws_probe.py

@@ -12,7 +12,9 @@ Usage::
         --send "hello"
 
 Options:
-    --url        ws://host:port/ws   (default ws://127.0.0.1:8790/ws)
+    --url        http(s)://host:port  (default http://127.0.0.1:8791)
+                 (legacy ws(s)://host:8790/ws URLs are still accepted and
+                 converted to the HTTP base automatically)
     --token      IRIS_TOKEN       (default: $IRIS_TOKEN)
     --device     device_id           (default: probe-<rand>)
     --send TEXT  send this message after pairing (default: "hello")
@@ -666,7 +668,7 @@ def run_http(args, base: str) -> int:
 
 def main() -> int:
     p = argparse.ArgumentParser(description=__doc__)
-    p.add_argument("--url", default=os.getenv("IRIS_WS_URL", "ws://127.0.0.1:8790/ws"))
+    p.add_argument("--url", default=os.getenv("IRIS_HTTP_URL", "http://127.0.0.1:8791"))
     p.add_argument("--token", default=os.getenv("IRIS_TOKEN", ""))
     p.add_argument("--device", default=f"probe-{uuid.uuid4().hex[:8]}")
     p.add_argument("--send", default="hello")
@@ -766,15 +768,17 @@ def main() -> int:
     if args.assert_read_receipt and not args.send:
         p.error("--assert-read-receipt requires --send (the receipt must follow the sent message)")
     # HTTP is the only transport (docs/19): derive the http(s) base from the
-    # --url (ws://host:8790/ws -> http://host:8791) unless --http-url is given.
+    # --url (legacy ws(s)://host:8790/ws -> http(s)://host:8791) unless
+    # --http-url is given.
     if args.http_url:
         base = args.http_url
     else:
         from urllib.parse import urlparse
 
         u = urlparse(args.url)
-        scheme = "https" if u.scheme == "wss" else "http"
-        base = f"{scheme}://{u.hostname or '127.0.0.1'}:8791"
+        scheme = "https" if u.scheme in ("wss", "https") else "http"
+        port = u.port or 8791
+        base = f"{scheme}://{u.hostname or '127.0.0.1'}:{port}"
     return run_http(args, base)