#183 fix(llm): compact on maximum image errors

A provider's maximum image-count error stops the run instead of enabling context compaction. This change recognizes that explicit refusal through the existing compaction path. It preserves rate-limit exclusions and existing retry limits. The classifier regression fails before this change and passes afterward. Existing overflow tests and all required typechecks pass.

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Summary by cubic

Classifies provider errors about exceeding the maximum image count as context overflow so the run compacts instead of stopping. Previously the error was treated as a hard failure; now it follows the same compaction path as token-limit errors, while rate-limit variants remain excluded.