- Add READ_TIMEOUT (5 min) and MAX_OUTPUT_SIZE (100 MB) constants
- Implement read_pipe_with_timeout() with watchdog thread protection
- Update execute_grep_command() to capture and return both streams
- Prevents TH-03 hang scenario by bounding both time and memory
Acceptance criteria:
✓ Stdout captured completely
✓ Stderr captured completely
✓ Output buffered without truncation (100 MB limit)
✓ Read operations have timeout protection (5 min timeout)
✓ Both streams captured even if one is empty
Verification: notes/bf-3wkpz.md
