feat(image-gen): honor image_gen.model from config.yaml in plugin dispatch

Image generation plugins were dispatched without a model name, leaving
the plugin to pick its default. Users on OpenRouter, ComfyUI, or custom
backends had no way to select a specific model through config — they
had to fork the plugin or patch the tool.

Add _read_configured_image_model() that reads image_gen.model from the
active profile's config.yaml and forwards it into
_dispatch_to_plugin_provider(). When model is set, the plugin call
gains a 'model' kwarg; when unset, the plugin falls back to its own
default, so single-model users see no behavior change.

Example config:

    image_gen:
      provider: openrouter
      model: flux-pro

Tests: all 170 image tool tests pass. The new code path is opt-in via
config and no existing test exercises it, so the change is strictly
additive.

tools/image_generation_tool.py

@@ -879,6 +879,21 @@ IMAGE_GENERATE_SCHEMA = {
 }
 
 
+def _read_configured_image_model():
+    """Return the value of ``image_gen.model`` from config.yaml, or None."""
+    try:
+        from hermes_cli.config import load_config
+        cfg = load_config()
+        section = cfg.get("image_gen") if isinstance(cfg, dict) else None
+        if isinstance(section, dict):
+            value = section.get("model")
+            if isinstance(value, str) and value.strip():
+                return value.strip()
+    except Exception as exc:
+        logger.debug("Could not read image_gen.model: %s", exc)
+    return None
+
+
 def _read_configured_image_provider():
     """Return the value of ``image_gen.provider`` from config.yaml, or None.
 
@@ -915,6 +930,9 @@ def _dispatch_to_plugin_provider(prompt: str, aspect_ratio: str):
     if not configured or configured == "fal":
         return None
 
+    # Also read configured model so we can pass it to the plugin
+    configured_model = _read_configured_image_model()
+
     try:
         # Import locally so plugin discovery isn't triggered just by
         # importing this module (tests rely on that).
@@ -950,7 +968,10 @@ def _dispatch_to_plugin_provider(prompt: str, aspect_ratio: str):
         })
 
     try:
-        result = provider.generate(prompt=prompt, aspect_ratio=aspect_ratio)
+        kwargs = {"prompt": prompt, "aspect_ratio": aspect_ratio}
+        if configured_model:
+            kwargs["model"] = configured_model
+        result = provider.generate(**kwargs)
     except Exception as exc:
         logger.warning(
             "Image gen provider '%s' raised: %s",