fix: deletion blocked

[sujaya-sys]

Overview

Attempt to fix #59

Note: I've been experimenting with claude code to solve this issue - if the implementation seems non-sensical or would take a long time to correct, please let me know so I can close the PR and add the issue back to our backlog. Thank you!

Summary of changes: Improved deletion logic to treat "not found" errors as successful deletion rather than blocking finalizer removal.

• Before: ANY deletion error blocks finalizer removal
• After: Only real infrastructure errors (network, auth) block finalizer removal

Change Summary

• 3 controllers updated: ApiCheck, Group, AlertChannel
• Added: isNotFoundError() utility function to detect 404/not found errors
• Added: unit tests
• Improved: ID validation (skip deletion attempts for empty IDs)

[sorccu]

Code looks alright to me and I don't think this should cause any issues, but again, not very familiar with the operator.