fix(seer): Capture GitLab webhook validation failures as exceptions

[billyvg]

Summary

When a GitLab merge_request or note webhook payload fails SeerCodeReviewTaskRequest validation, _schedule_task drops the review entirely — it never reaches Seer, yet GitLab still receives a 200. Today this is only a debug_log at WARNING level, so the silent drops are effectively invisible.

This replaces the validation_failed / note.validation_failed debug logs with sentry_sdk.capture_exception, so a dropped review surfaces as a Sentry issue and can be triaged.

Changes

• Both except ValidationError blocks (MR-event path and @sentry review note path) now capture_exception(e) inside a scope that carries the validation_errors and seer_path (or mr_iid) as context for triage.
• record_webhook_filtered(..., INVALID_PAYLOAD) is retained — the metric is still useful.

Why

A validation failure is not a benign "filtered" event — it means we accepted the webhook but never ran the review the customer expected. That deserves escalation, not a debug log. (This is the same failure mode behind the trigger_at datetime bug; see related PR.)

Tests

• test_validation_failure_is_captured_and_review_dropped — forces a ValidationError, asserts capture_exception is called with it and the Seer task is not enqueued.

Note

Independent of (not stacked on) the trigger_at normalization PR — they touch different code paths in the same file and can merge in any order.

🤖 Generated with Claude Code

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