chore: update drain3 default log pattern weights

[github-actions]

This pull request updates the default Drain3 log pattern weights (pkg/agentdrain/data/default_weights.json) by training on the most recent workflow run logs.

What changed

• Re-trained log template clusters from the latest run logs using gh aw logs --train
• Copied resulting drain3_weights.json to the embedded defaults path

How to verify

1. Build the binary with make build
2. Run gh aw audit or gh aw logs --train and confirm the anomaly analysis reflects the updated patterns

This PR was created automatically by the train-drain3-weights workflow.