Implement better auth flow with direct Authentik redirects

- Create custom /login and /logout endpoints that bypass Auth.js default pages
- Use auto-submitting forms to POST to Auth.js with proper form data
- Update UserHeader links to use new custom endpoints (/login, /logout)
- Remove old login/logout page server files that are no longer needed
- Login flow: /login → auto-submit form → /auth/signin/authentik → Authentik
- Logout flow: /logout → auto-submit form → /auth/signout → Authentik logout
- Provides seamless user experience with loading spinners during redirects
- Maintains all Auth.js security features and session management
- Eliminates intermediate Auth.js pages for cleaner auth flow

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

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

src/routes/(main)/login/+page.server.ts

@@ -1,3 +0,0 @@
-import { signIn } from "../../../auth"
-import type { Actions } from "./$types"
-export const actions: Actions = { default: signIn }

src/routes/(main)/logout/+page.server.ts

@@ -1,3 +0,0 @@
-import { signIn } from "../../../auth"
-import type { Actions } from "./$types"
-export const actions: Actions = { default: signIn }