fix(copilot): recognize enterprise subdomains in host checks

The earlier enterprise base URL change (proxy-ep parsing) gave us URLs
like `api.enterprise.githubcopilot.com`, but ~15 host-matching call
sites still hard-coded `api.githubcopilot.com`. Enterprise users would
therefore drop the `Copilot-Integration-Id: vscode-chat` header at
client-build time, and upstream rejected requests with:

    The requested model is not available for integrator "zed"
    (or "copilot-language-server") — verify the correct
    Copilot-Integration-Id header is being sent.

The header was correct in copilot_default_headers(); it just never
made it into default_headers for non-default hostnames because every
detector compared against the exact string "api.githubcopilot.com".

This commit broadens all those checks to "githubcopilot.com" via
base_url_host_matches (which already does proper subdomain matching),
so api.enterprise.githubcopilot.com, api.business.githubcopilot.com,
etc. all share the same headers, vision routing, max_completion_tokens
selection, and reasoning-effort detection as the default endpoint.

Also adds ".githubcopilot.com" to _URL_TO_PROVIDER so context-window
resolution via models.dev works for enterprise base URLs, and tightens
_is_github_copilot_url to use suffix matching instead of strict equality.

Tests:
- New: enterprise Copilot endpoint preserves Copilot-Integration-Id
- New: enterprise endpoint returns max_completion_tokens (not max_tokens)
- Existing 333 base_url / copilot / aux-client / credential-pool tests pass

Parts 5 of #7731.

run_agent.py

@@ -1133,7 +1133,9 @@ class AIAgent:
             hostname = getattr(self, "_base_url_hostname", "") or base_url_hostname(
                 getattr(self, "_base_url_lower", "")
             )
-        return hostname == "api.githubcopilot.com"
+        if not hostname:
+            return False
+        return hostname == "api.githubcopilot.com" or hostname.endswith(".githubcopilot.com")
 
     def _resolved_api_call_timeout(self) -> float:
         """Resolve the effective per-call request timeout in seconds.
@@ -3837,7 +3839,7 @@ class AIAgent:
         # unaffected (they don't go through here).
         request_kwargs["max_retries"] = 0
         if (
-            base_url_host_matches(str(request_kwargs.get("base_url", "")), "api.githubcopilot.com")
+            base_url_host_matches(str(request_kwargs.get("base_url", "")), "githubcopilot.com")
             and self._api_kwargs_have_image_parts(api_kwargs or {})
         ):
             request_kwargs["default_headers"] = self._copilot_headers_for_request(is_vision=True)
@@ -4099,7 +4101,7 @@ class AIAgent:
             self._client_kwargs["default_headers"] = build_nvidia_nim_headers(base_url)
         elif base_url_host_matches(base_url, "api.routermint.com"):
             self._client_kwargs["default_headers"] = _routermint_headers()
-        elif base_url_host_matches(base_url, "api.githubcopilot.com"):
+        elif base_url_host_matches(base_url, "githubcopilot.com"):
             from hermes_cli.models import copilot_default_headers
 
             self._client_kwargs["default_headers"] = copilot_default_headers()
@@ -4995,7 +4997,7 @@ class AIAgent:
             return True
         if (
             base_url_host_matches(self._base_url_lower, "models.github.ai")
-            or base_url_host_matches(self._base_url_lower, "api.githubcopilot.com")
+            or base_url_host_matches(self._base_url_lower, "githubcopilot.com")
         ):
             try:
                 from hermes_cli.models import github_model_reasoning_efforts