Add job run logs, OpenRouter model picker, and discipline grouping.

- Job logs: each job's stdout/stderr is teed into outputs/<id>/job.log
  (survives restarts) and served at GET /jobs/{id}/log as text/plain, so
  full run logs can be shared for debugging and refinement.
- Model picker: GET /models proxies OpenRouter's public model list with
  per-1M-token pricing (1h cache, 502 on failure); the UI shows a model
  dropdown with costs when OpenRouter compute is selected, and the pick
  overrides vision+text models for that job (Classic and Agent modes).
- Conflicts in the report view are grouped by discipline pair
  (collapsible sections, severity-ordered within groups) instead of one
  flat severity-only list.

backend/llm.py

@@ -24,6 +24,16 @@ _clients: Dict[str, OpenAI] = {}
 # set_stage/cost pattern (single-user tool).
 _text_local = False
 
+# Per-job model override (user picked a model in the UI). Same module-global
+# pattern: set by the job runner before the pipeline starts, cleared after.
+_model_override: Optional[str] = None
+
+
+def set_model_override(model: Optional[str]) -> None:
+    """Override the model for all OpenRouter calls (vision + text), or None to clear."""
+    global _model_override
+    _model_override = (model or "").strip() or None
+
 
 def set_text_backend(local: bool) -> None:
     """Choose whether text (no-image) calls go to the local endpoint this run."""
@@ -171,12 +181,13 @@ def _resolve_backend(has_images: bool, model_override: Optional[str]) -> Dict[st
             "usage": False,          # local has no OpenRouter usage accounting
             "local": True,
         }
-    # Vision, or text-on-OpenRouter (default / fallback).
+    # Vision, or text-on-OpenRouter (default / fallback). A per-job override
+    # (user's UI model pick) wins over per-call and env defaults.
     default_model = config.MODEL if has_images else config.TEXT_MODEL
     return {
         "base_url": config.AI_BASE_URL,
         "api_key": config.AI_API_KEY,
-        "model": model_override or default_model,
+        "model": _model_override or model_override or default_model,
         "usage": True,
         "local": False,
     }