Expose OAuth and account providers in onboarding

The provider step was filtered to API_KEY only, which hid GitHub
Copilot, Google Antigravity, and GPT account from the founding-CEO
runtime picker even though they are first-class providers in the
catalog. Show every non-cloud provider, render an "Access token" field
in place of the API-key field for OAuth and account auths, and surface
a button that opens the provider's official sign-in page via the new
openExternalUrl IPC (validated to http(s) only).

OnboardingService.resolveProvider now accepts any non-cloud auth type.
Cloud providers still route through Settings since their multi-field
config does not fit the linear onboarding step.

AgentCompany-New/src/preload/index.ts

@@ -22,6 +22,7 @@ const api: DesktopApi = {
   markChatSpaceRead: (input) => invoke(IPC_CHANNELS.markChatSpaceRead, input),
   saveProviderCredential: (input) => invoke(IPC_CHANNELS.saveProviderCredential, input),
   launchProviderSignIn: (input) => invoke(IPC_CHANNELS.launchProviderSignIn, input),
+  openExternalUrl: (url) => invoke(IPC_CHANNELS.openExternalUrl, url),
   createProviderResponse: (input) => invoke(IPC_CHANNELS.createProviderResponse, input),
   importSkillDirectory: (input) => invoke(IPC_CHANNELS.importSkillDirectory, input),
   bindSkill: (input) => invoke(IPC_CHANNELS.bindSkill, input),