feat: make tool-use enforcement configurable via agent.tool_use_enforcement (#3551)

The TOOL_USE_ENFORCEMENT_GUIDANCE injection (added in #3528) was
hardcoded to only match gpt/codex model names. This makes it a
config option so users can turn it on for any model family.

New config key: agent.tool_use_enforcement
  - "auto" (default): matches gpt/codex (existing behavior)
  - true: inject for all models
  - false: never inject
  - list of strings: custom model-name substrings to match
    e.g. ["gpt", "codex", "deepseek", "qwen"]

No version bump needed — deep merge provides the default
automatically for existing installs.

12 new tests covering all config modes.

hermes_cli/config.py

@@ -138,6 +138,12 @@ DEFAULT_CONFIG = {
     "toolsets": ["hermes-cli"],
     "agent": {
         "max_turns": 90,
+        # Tool-use enforcement: injects system prompt guidance that tells the
+        # model to actually call tools instead of describing intended actions.
+        # Values: "auto" (default — applies to gpt/codex models), true/false
+        # (force on/off for all models), or a list of model-name substrings
+        # to match (e.g. ["gpt", "codex", "gemini", "qwen"]).
+        "tool_use_enforcement": "auto",
     },
     
     "terminal": {