Fixes two spec-implementation discrepancies identified in issue #5009:
1. Checkpoint trigger names: rename on_tool_write → before_tool_execute and
on_tool_write_complete → after_tool_execute to match the implementation in
src/cleveragents/tool/runner.py and src/cleveragents/application/services/
config_service.py. The implementation names are more precise — they describe
the execution phase rather than implying only write tools trigger them
(though the implementation correctly gates them on write tools).
2. Config key path: correct the Configuration Reference table entry from
sandbox.checkpoint.auto-create-on to core.checkpoints.auto-create-on,
matching both the implementation (config_service.py line 482) and the
inline spec at line 19449. Also update the default values in the table
to use the corrected trigger names.
Closes#5009