[WIP] Fix sync service with OAuth and GitHub App authentication

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

---

This section details on the original issue you should resolve

<issue_title>bug: sync service with OAuth/GitHub App authentication</issue_title>
<issue_description>Major parts of the sync service are disrupted when when using OAuth [for user authentication] or a GitHub App [for github api authentication].

sync cronjob

The sync cronjob/container's entrypoint code only checks for a github PAT (in process.env.NUXT_GITHUB_TOKEN):

copilot-metrics-viewer/server/sync-entry.ts

Lines 41 to 45 in b1112bf

	if (!githubToken) {
	logger.error('NUXT_GITHUB_TOKEN environment variable is required');
	process.exit(1);
	return; // guard: allows tests to mock process.exit without continuing
	}

and does not respect the presence of NUXT_GITHUB_APP_ID and NUXT_GITHUB_APP_PRIVATE_KEY when present. The authentication middleware isn't invoked to create headers, creating them manually instead. In theory, this should be an easy update to expand the checks and calling the auth middleware to init headers, which will handle selecting the right auth.

/api/admin/sync endpoint

When any external auth provider is configured, calls to the /api/admin/sync endpoint will be rejected without a valid user session.

The docs make it sound like it should support pass-through auth, and I think it does, but it's not getting this far due to the authentication middleware:

copilot-metrics-viewer/server/middleware/github.ts

Line 31 in b1112bf

const requireAuth = config.public.requireAuth || config.public.usingGithubAuth || config.public.isPublicApp || !!config.public.authProviders;

I'm not sure what the intended use of this was supposed to be when user auth is enabled. Should a sync token value be implemented in these cases? Should a special handler skip OAuth and allow pass-through auth?

Happy to PR for either with some direction.</issue_description>

<agent_instructions>Please investigate and suggest changes</agent_instructions>

Comments on the Issue (you are @copilot in this section)

[karpikpl]

@copilot investigate failing build