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.

[github-actions]

Hey @github-actions[bot] 👋 — thanks for the automated Drain3 weight refresh! Keeping the default log pattern weights up-to-date is essential for accurate anomaly detection, so this kind of housekeeping PR is a great fit for the project.

One checklist item flagged mechanically:

• No test file changes — the diff only touches pkg/agentdrain/data/default_weights.json. For a pure data-file retrain this is expected and likely fine, but if there are snapshot or golden-file tests that should be regenerated alongside the weights, it would be worth confirming they're still in sync.

If a test refresh is needed, an agent can handle it:

Review the test suite under pkg/agentdrain/ for any snapshot, golden-file, or integration tests that reference default_weights.json or drain3 pattern templates.
If any tests need to be updated to reflect the newly trained weights in pkg/agentdrain/data/default_weights.json, apply the necessary updates and verify all tests pass with `make test`.

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