Harden job payload parsing: kwarg-mismatch silently drops jobs

[jerry7991]

Problem

bin/nebula_queue_worker:103:

handler_class.new.perform(**payload['args'].transform_keys(&:to_sym))

Two issues:

1. Kwarg signature mismatch drops jobs. If a payload contains a key the handler doesn't declare (e.g., producer added tracking_id: before consumer was deployed), perform raises ArgumentError: unknown keyword and the rescue at line 106 logs + drops it. No retry, no DLQ. Rolling deploys of producer → consumer will silently lose jobs.
2. transform_keys(&:to_sym) on arbitrary JSON. Modern Ruby GCs symbols, but combined with (1) this amplifies silent loss. Also, no schema validation — nothing rejects payloads missing required args or with wrong types; the error surfaces only at perform call time.

Fix

• Use perform(**args, **_ignored) pattern, or explicitly filter the payload hash to the method signature (method(:perform).parameters) and log/reject unknown keys instead of dropping.
• Validate payload shape (job, args, enqueued_at, retry_count) at fetch time; malformed payloads go straight to the dead set with a MalformedPayload reason.
• Pair with the retry/DLQ work — any handler exception (including ArgumentError) must be retried, not dropped.

Acceptance

• Adding a new kwarg to a producer without restarting consumers does not lose jobs.
• Malformed payloads appear in a dead-letter / failed set, not just stderr.