fix(copilot): add missing Copilot-Integration-Id header

The GitHub Copilot API now requires a Copilot-Integration-Id header
on all requests. Without it, every API call fails with HTTP 400:
"missing required Copilot-Integration-Id header".

Uses vscode-chat as the integration ID, matching opencode which
shares the same OAuth client ID (Ov23li8tweQw6odWQebz).

Fixes: Copilot provider fails with "missing required Copilot-Integration-Id header" (HTTP 400)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

hermes_cli/copilot_auth.py

@@ -285,6 +285,7 @@ def copilot_request_headers(
     headers: dict[str, str] = {
         "Editor-Version": "vscode/1.104.1",
         "User-Agent": "HermesAgent/1.0",
+        "Copilot-Integration-Id": "vscode-chat",
         "Openai-Intent": "conversation-edits",
         "x-initiator": "agent" if is_agent_turn else "user",
     }