fix: compaction now triggers correctly and supports fixed token limit

- Lower COMPACT_PRESERVE_RECENT from 6 to 1 so compaction can trigger
  after just 2 messages instead of requiring 8+
- Add MORPH_COMPACT_TOKEN_LIMIT env var to override percentage-based
  threshold with a fixed token count
- Fix minimum message guard: was `< PRESERVE_RECENT + 2`, now
  `<= PRESERVE_RECENT` so compaction works with fewer exchanges
- Bump morphsdk to ^0.2.148
- Add detailed logging for compaction decisions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>