feat: OpenAI-compatible API server + WhatsApp configurable reply prefix (#1756)

* feat: OpenAI-compatible API server platform adapter

Salvaged from PR #956, updated for current main.

Adds an HTTP API server as a gateway platform adapter that exposes
hermes-agent via the OpenAI Chat Completions and Responses APIs.
Any OpenAI-compatible frontend (Open WebUI, LobeChat, LibreChat,
AnythingLLM, NextChat, ChatBox, etc.) can connect by pointing at
http://localhost:8642/v1.

Endpoints:
- POST /v1/chat/completions  — stateless Chat Completions API
- POST /v1/responses         — stateful Responses API with chaining
- GET  /v1/responses/{id}    — retrieve stored response
- DELETE /v1/responses/{id}  — delete stored response
- GET  /v1/models            — list hermes-agent as available model
- GET  /health               — health check

Features:
- Real SSE streaming via stream_delta_callback (uses main's streaming)
- In-memory LRU response store for Responses API conversation chaining
- Named conversations via 'conversation' parameter
- Bearer token auth (optional, via API_SERVER_KEY)
- CORS support for browser-based frontends
- System prompt layering (frontend system messages on top of core)
- Real token usage tracking in responses

Integration points:
- Platform.API_SERVER in gateway/config.py
- _create_adapter() branch in gateway/run.py
- API_SERVER_* env vars in hermes_cli/config.py
- Env var overrides in gateway/config.py _apply_env_overrides()

Changes vs original PR #956:
- Removed streaming infrastructure (already on main via stream_consumer.py)
- Removed Telegram reply_to_mode (separate feature, not included)
- Updated _resolve_model() -> _resolve_gateway_model()
- Updated stream_callback -> stream_delta_callback
- Updated connect()/disconnect() to use _mark_connected()/_mark_disconnected()
- Adapted to current Platform enum (includes MATTERMOST, MATRIX, DINGTALK)

Tests: 72 new tests, all passing
Docs: API server guide, Open WebUI integration guide, env var reference

* feat(whatsapp): make reply prefix configurable via config.yaml

Reworked from PR #1764 (ifrederico) to use config.yaml instead of .env.

The WhatsApp bridge prepends a header to every outgoing message.
This was hardcoded to '⚕ *Hermes Agent*'. Users can now customize
or disable it via config.yaml:

  whatsapp:
    reply_prefix: ''                     # disable header
    reply_prefix: '🤖 *My Bot*\n───\n'  # custom prefix

How it works:
- load_gateway_config() reads whatsapp.reply_prefix from config.yaml
  and stores it in PlatformConfig.extra['reply_prefix']
- WhatsAppAdapter reads it from config.extra at init
- When spawning bridge.js, the adapter passes it as
  WHATSAPP_REPLY_PREFIX in the subprocess environment
- bridge.js handles undefined (default), empty (no header),
  or custom values with \\n escape support
- Self-chat echo suppression uses the configured prefix

Also fixes _config_version: was 9 but ENV_VARS_BY_VERSION had a
key 10 (TAVILY_API_KEY), so existing users at v9 would never be
prompted for Tavily. Bumped to 10 to close the gap. Added a
regression test to prevent this from happening again.

Credit: ifrederico (PR #1764) for the bridge.js implementation
and the config version gap discovery.

---------

Co-authored-by: Test <test@test.com>

gateway/platforms/whatsapp.py

@@ -136,6 +136,7 @@ class WhatsAppAdapter(BasePlatformAdapter):
             "session_path",
             get_hermes_home() / "whatsapp" / "session"
         ))
+        self._reply_prefix: Optional[str] = config.extra.get("reply_prefix")
         self._message_queue: asyncio.Queue = asyncio.Queue()
         self._bridge_log_fh = None
         self._bridge_log: Optional[Path] = None
@@ -193,6 +194,14 @@ class WhatsAppAdapter(BasePlatformAdapter):
             self._bridge_log = self._session_path.parent / "bridge.log"
             bridge_log_fh = open(self._bridge_log, "a")
             self._bridge_log_fh = bridge_log_fh
+
+            # Build bridge subprocess environment.
+            # Pass WHATSAPP_REPLY_PREFIX from config.yaml so the Node bridge
+            # can use it without the user needing to set a separate env var.
+            bridge_env = os.environ.copy()
+            if self._reply_prefix is not None:
+                bridge_env["WHATSAPP_REPLY_PREFIX"] = self._reply_prefix
+
             self._bridge_process = subprocess.Popen(
                 [
                     "node",
@@ -204,6 +213,7 @@ class WhatsAppAdapter(BasePlatformAdapter):
                 stdout=bridge_log_fh,
                 stderr=bridge_log_fh,
                 preexec_fn=None if _IS_WINDOWS else os.setsid,
+                env=bridge_env,
             )
             
             # Wait for the bridge to connect to WhatsApp.