Add protect_first_n and protect_last_n to the compression config section
in config.yaml, allowing users to control how many initial and recent
turns are preserved during context compression.
- Default values: protect_first_n=3, protect_last_n=4 (no behavior change)
- Values clamped to 0-12 range (inspired by openclaw recentTurnsPreserve)
- Config version bumped to 6 for migration
- Also improved run_agent.py to read compression config from config.yaml
(previously only read from env vars)
Related: #525 (microcompact)
