feat(server): add client IP to auth-related log messages

[nijdarshan]

Summary

• Adds a ClientIP helper function that extracts the real client IP from HTTP requests (checking X-Forwarded-For, X-Real-IP, then RemoteAddr)
• Includes client IP in OIDC token verification failures, login flow errors, and auth middleware warnings
• Helps administrators identify which clients are flooding logs with authentication errors

Test plan

• Unit tests for ClientIP helper covering all header combinations
• go build passes on all affected packages
• golangci-lint passes on affected packages
• CI passes

Fixes #20388

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[choejwoo]

Could this also cover OIDC-related CLI flows over gRPC (e.g., argocd login --sso)? From a quick look, it seems IP is extracted only from HTTP requests, so pure gRPC calls may not be logged.
Also, since PR #25991 already adds client address to token verification errors, is there a reason to open a new PR?