feat(sponsor-panel): add Patreon OAuth login support (#1179)
* feat(sponsor-panel): add Patreon OAuth login support
Add Patreon as a second authentication provider so patrons get the same
features as GitHub Sponsors (Discord invite, team invitations, logo
submissions). Uses Patreon API v2 for identity and membership
verification via direct HTTP calls, with patreon-go for OAuth constants.
- Add optional Patreon OAuth flags (service works GitHub-only if omitted)
- Add database migration for patreon_id, provider columns
- Create patreon_oauth.go with login/callback handlers
- Update login page with conditional Patreon button
- Update dashboard to show provider-appropriate sponsor links
- Patreon users are separate identities, same tier-gated features
* feat(sponsor-panel): add --patreon-fifty-plus flag for blessed patrons
Adds a flag to bless Patreon usernames with the $50/month tier,
mirroring the existing --fifty-plus-sponsors flag for GitHub users.
Also adds debug logging for Patreon identity and membership data.