fix(copilot): normalize vendor-prefixed and dash-notation model IDs (#6879) (#11561)

The Copilot API returns HTTP 400 "model_not_supported" when it receives a
model ID it doesn't recognize (vendor-prefixed like
`anthropic/claude-sonnet-4.6` or dash-notation like `claude-sonnet-4-6`).
Two bugs combined to leave both formats unhandled:

1. `_COPILOT_MODEL_ALIASES` in hermes_cli/models.py only covered bare
   dot-notation and vendor-prefixed dot-notation.  Hermes' default Claude
   IDs elsewhere use hyphens (anthropic native format), and users with an
   aggregator-style config who switch `model.provider` to `copilot`
   inherit `anthropic/claude-X-4.6` — neither case was in the table.

2. The Copilot branch of `normalize_model_for_provider()` only stripped
   the vendor prefix when it matched the target provider (`copilot/`) or
   was the special-cased `openai/` for openai-codex.  Every other vendor
   prefix survived to the Copilot request unchanged.

Fix:

- Add dash-notation aliases (`claude-{opus,sonnet,haiku}-4-{5,6}` and the
  `anthropic/`-prefixed variants) to the alias table.
- Rewire the Copilot / Copilot-ACP branch of
  `normalize_model_for_provider()` to delegate to the existing
  `normalize_copilot_model_id()`.  That function already does alias
  lookups, catalog-aware resolution, and vendor-prefix fallback — it was
  being bypassed for the generic normalisation entry point.

Because `switch_model()` already calls `normalize_model_for_provider()`
for every `/model` switch (line 685 in model_switch.py), this single fix
covers the CLI startup path (cli.py), the `/model` slash command path,
and the gateway load-from-config path.

Closes #6879

Credits dsr-restyn (#6743) who independently diagnosed the dash-notation
case; their aliases are folded into this consolidated fix alongside the
vendor-prefix stripping repair.

hermes_cli/model_normalize.py

@@ -374,7 +374,26 @@ def normalize_model_for_provider(model_input: str, target_provider: str) -> str:
             return bare
         return _dots_to_hyphens(bare)
 
-    # --- Copilot: strip matching provider prefix, keep dots ---
+    # --- Copilot / Copilot ACP: delegate to the Copilot-specific
+    #     normalizer.  It knows about the alias table (vendor-prefix
+    #     stripping for Anthropic/OpenAI, dash-to-dot repair for Claude)
+    #     and live-catalog lookups.  Without this, vendor-prefixed or
+    #     dash-notation Claude IDs survive to the Copilot API and hit
+    #     HTTP 400 "model_not_supported".  See issue #6879.
+    if provider in {"copilot", "copilot-acp"}:
+        try:
+            from hermes_cli.models import normalize_copilot_model_id
+
+            normalized = normalize_copilot_model_id(name)
+            if normalized:
+                return normalized
+        except Exception:
+            # Fall through to the generic strip-vendor behaviour below
+            # if the Copilot-specific path is unavailable for any reason.
+            pass
+
+    # --- Copilot / Copilot ACP / openai-codex fallback:
+    #     strip matching provider prefix, keep dots ---
     if provider in _STRIP_VENDOR_ONLY_PROVIDERS:
         stripped = _strip_matching_provider_prefix(name, provider)
         if stripped == name and name.startswith("openai/"):