fix: Change auth blueprint prefix from /admin to /auth (v0.9.2)

The auth routes were registered under /admin/* but the IndieAuth
redirect_uri was configured as /auth/callback, causing 404 errors
when providers redirected back after authentication.

- Change auth blueprint url_prefix from "/admin" to "/auth"
- Update test expectations for new auth route paths
- Add ADR-022 documenting the architectural decision

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.9.2] - 2025-11-22
+
+### Fixed
+- **IndieAuth callback 404 error**: Fixed auth blueprint URL prefix mismatch
+  - Auth blueprint was using `/admin` prefix but redirect_uri used `/auth/callback`
+  - Changed blueprint prefix from `/admin` to `/auth` as documented in ADR-022
+  - Auth routes now correctly at `/auth/login`, `/auth/callback`, `/auth/logout`
+  - Admin dashboard routes remain at `/admin/*` (unchanged)
+
+### Changed
+- Updated test expectations to use new `/auth/*` URL patterns
+
 ## [0.9.1] - 2025-11-19
 
 ### Fixed