feat(oauth2): add image URL support for OAuth2 clients

[forkline-bot]

Summary

• Add image field to KanidmOAuth2ClientSpec with URL configuration
• Add OAuth2ClientImageStatus for caching image metadata (ETag, hash, size)
• Add image.rs module with download and validation logic
• Add image reconciliation with change detection via HEAD requests
• Support content types: png, jpg, gif, svg, webp
• Enforce max size of 256KB

Implementation Details

• Uses HEAD requests for efficient change detection (ETag, Last-Modified, Content-Length)
• Only downloads images when changes are detected
• Stores image metadata in status to survive operator restarts
• Surfaces HTTP errors via Kubernetes Events

Resolves: #567

[pando85]

@forkline fix fmt and clippy

[forkline-bot]

Fixed formatting issues in libs/oauth2/src/image.rs, libs/oauth2/src/reconcile/mod.rs, and libs/oauth2/src/reconcile/status.rs. Both cargo fmt and cargo clippy now pass. Pushed commit 92ec2e9 to branch feat/567-oauth2-image-support.

[pando85]

@forkline fix previous commit. Follow commit lint. It has to start with uppercase the title after the tag

[pando85]

@forkline fix previous commit. Follow commit lint. It has to start with uppercase the title after the tag

[forkline-bot]

Fixed. Commit message amended to fix: Apply cargo fmt to oauth2 image support code and pushed to feat/567-oauth2-image-support.