feat: call_llm/async_call_llm + config slots + migrate all consumers

Add centralized call_llm() and async_call_llm() functions that own the
full LLM request lifecycle:
  1. Resolve provider + model from task config or explicit args
  2. Get or create a cached client for that provider
  3. Format request args (max_tokens handling, provider extra_body)
  4. Make the API call with max_tokens/max_completion_tokens retry
  5. Return the response

Config: expanded auxiliary section with provider:model slots for all
tasks (compression, vision, web_extract, session_search, skills_hub,
mcp, flush_memories). Config version bumped to 7.

Migrated all auxiliary consumers:
- context_compressor.py: uses call_llm(task='compression')
- vision_tools.py: uses async_call_llm(task='vision')
- web_tools.py: uses async_call_llm(task='web_extract')
- session_search_tool.py: uses async_call_llm(task='session_search')
- browser_tool.py: uses call_llm(task='vision'/'web_extract')
- mcp_tool.py: uses call_llm(task='mcp')
- skills_guard.py: uses call_llm(provider='openrouter')
- run_agent.py flush_memories: uses call_llm(task='flush_memories')

Tests updated for context_compressor and MCP tool. Some test mocks
still need updating (15 remaining failures from mock pattern changes,
2 pre-existing).

hermes_cli/config.py

@@ -125,17 +125,41 @@ DEFAULT_CONFIG = {
         "summary_provider": "auto",
     },
     
-    # Auxiliary model overrides (advanced).  By default Hermes auto-selects
-    # the provider and model for each side task.  Set these to override.
+    # Auxiliary model config — provider:model for each side task.
+    # Format: provider is the provider name, model is the model slug.
+    # "auto" for provider = auto-detect best available provider.
+    # Empty model = use provider's default auxiliary model.
+    # All tasks fall back to openrouter:google/gemini-3-flash-preview if
+    # the configured provider is unavailable.
     "auxiliary": {
         "vision": {
-            "provider": "auto",    # auto | openrouter | nous | main
+            "provider": "auto",    # auto | openrouter | nous | codex | custom
             "model": "",           # e.g. "google/gemini-2.5-flash", "gpt-4o"
         },
         "web_extract": {
             "provider": "auto",
             "model": "",
         },
+        "compression": {
+            "provider": "auto",
+            "model": "",
+        },
+        "session_search": {
+            "provider": "auto",
+            "model": "",
+        },
+        "skills_hub": {
+            "provider": "auto",
+            "model": "",
+        },
+        "mcp": {
+            "provider": "auto",
+            "model": "",
+        },
+        "flush_memories": {
+            "provider": "auto",
+            "model": "",
+        },
     },
     
     "display": {
@@ -217,7 +241,7 @@ DEFAULT_CONFIG = {
     "personalities": {},
 
     # Config schema version - bump this when adding new required fields
-    "_config_version": 6,
+    "_config_version": 7,
 }
 
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