#460 MEDIUM: Performance bottlenecks in hot paths

1. N+1 activity queries (activity_logger.py:519) - HIGH 2. O(N²) variable lookups in loops (inline_executor.py) - HIGH 3. Excessive debug logging (62 files) - MEDIUM 4. JSON parsing without cache (variable_resolver.py:303-308) - MEDIUM 5. Inefficient batch init (inline_executor.py:393-401) - MEDIUM