fix: complete already removed temporary bans

[vycdev2]

Summary

• stop retrying expired temporary bans when Discord confirms the ban was already removed
• distinguish the Unknown Ban 404 from other missing-resource errors so unrelated failures remain pending for retry
• add regression coverage for both outcomes

Verification

• dotnet build — passed (0 errors; existing SQLitePCLRaw NU1903 warning)
• dotnet test --no-build --filter 'FullyQualifiedName~TemporaryBansJobTests' --logger 'console;verbosity=minimal' — passed (3/3)
• dotnet test --no-build --logger 'console;verbosity=minimal' — 299 passed, 2 failed because this runner cannot load tr-TR in globalization-invariant mode; the failures are in unchanged MiscModuleTests and are tracked by PR test: skip unavailable culture regression #81
• git diff --check upstream/develop...HEAD — passed

Risk

• Low: only Discord Unknown Ban 404 responses are treated as completed; all other errors keep the existing retry behavior.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.