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/adapter.py

@@ -45,14 +45,14 @@ Configuration in config.yaml::
           enabled: true
           extra:
             host: 127.0.0.1
-            port: 8790
+            http_port: 8791
             home_channel: default
             push_backend: fcm
             outbox_retention_hours: 72
             max_upload_bytes: 104857600
 
 Or via environment variables (overrides config.yaml; secrets live in .env):
-    IRIS_TOKEN, IRIS_WS_HOST, IRIS_WS_PORT, IRIS_HOME_CHANNEL,
+    IRIS_TOKEN, IRIS_HTTP_HOST, IRIS_HTTP_PORT, IRIS_HOME_CHANNEL,
     IRIS_PUSH_BACKEND, IRIS_FCM_SERVICE_ACCOUNT, NTFY_TOPIC, ...
 """
 
@@ -175,9 +175,8 @@ class IrisAdapter(
 
         extra = getattr(config, "extra", {}) or {}
 
-        # Connection settings (env vars override config.yaml). The bind host
-        # is shared with the (legacy) WS-era env var name for compatibility.
-        self.host = os.getenv("IRIS_WS_HOST", "").strip() or extra.get("host", DEFAULT_HOST)
+        # Connection settings (env vars override config.yaml).
+        self.host = os.getenv("IRIS_HTTP_HOST", "").strip() or extra.get("host", DEFAULT_HOST)
         # docs/19: HTTP transport (the only device-facing transport; optional TLS).
         self.http_port = _parse_port(
             os.getenv("IRIS_HTTP_PORT", "") or str(extra.get("http_port", DEFAULT_HTTP_PORT))