feat: API server model name derived from profile name (#6857)

* feat: API server model name derived from profile name

For multi-user setups (e.g. OpenWebUI), each profile's API server now
advertises a distinct model name on /v1/models:

- Profile 'lucas' -> model ID 'lucas'
- Profile 'admin' -> model ID 'admin'
- Default profile -> 'hermes-agent' (unchanged)

Explicit override via API_SERVER_MODEL_NAME env var or
platforms.api_server.model_name config for custom names.

Resolves friction where OpenWebUI couldn't distinguish multiple
hermes-agent connections all advertising the same model name.

* docs: multi-user setup with profiles for API server + Open WebUI

- api-server.md: added Multi-User Setup section, API_SERVER_MODEL_NAME
  to config table, updated /v1/models description
- open-webui.md: added Multi-User Setup with Profiles section with
  step-by-step guide, updated model name references
- environment-variables.md: added API_SERVER_MODEL_NAME entry

hermes_cli/config.py

@@ -1216,6 +1216,14 @@ OPTIONAL_ENV_VARS = {
         "category": "messaging",
         "advanced": True,
     },
+    "API_SERVER_MODEL_NAME": {
+        "description": "Model name advertised on /v1/models. Defaults to the profile name (or 'hermes-agent' for the default profile). Useful for multi-user setups with OpenWebUI.",
+        "prompt": "API server model name",
+        "url": None,
+        "password": False,
+        "category": "messaging",
+        "advanced": True,
+    },
     "WEBHOOK_ENABLED": {
         "description": "Enable the webhook platform adapter for receiving events from GitHub, GitLab, etc.",
         "prompt": "Enable webhooks (true/false)",