verify: The ops "How to manage actions" doc shows a snapshot action handler th

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The ops "How to manage actions" doc shows a snapshot action handler that ends with event.set_results({'result': msg}) — so the action results dict contains the key result, with a value like "Stored snapshot in db-snapshot.tar.gz.". The very next code block, the unit test, asserts 'snapshot-size' in ctx.action_results. I believe the doc is wrong here: the handler never sets a snapshot-size key, so that assertion would fail.

I implemented the snapshot action in the kepler charm exactly as the doc describes (log a message, do the snapshot, then event.set_results({'result': msg})), and added a test that asserts my understanding: that 'snapshot-size' is NOT in ctx.action_results (and that the results are exactly {'result': 'Stored snapshot in db-snapshot.tar.gz.'}). This test is expected to pass.

If CI passes, the doc's example unit test is incorrect — the documented assertion 'snapshot-size' in ctx.action_results does not hold against the documented handler, because the handler sets result, not snapshot-size. If CI fails (i.e., snapshot-size somehow IS in the results), then the doc's test would pass and the doc would be correct — but I'd be surprised, since nothing in the shown handler produces that key.

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This PR is a draft. Inspect the changes, then mark it ready for review to run CI.