docs(roadmap): add #330 — resume mode stats/cost always zero

[code-yeongyu]

Pinpoint #324

Gap: claw --output-format json --resume latest /stats and /cost always return zero token counts.

Live reproduction on e7074f4:

claw --output-format json --resume latest /stats
# → {"input_tokens": 0, "output_tokens": 0, "total_tokens": 0, ...}

claw --output-format json --resume latest /cost  
# → {"input_tokens": 0, "output_tokens": 0, "total_tokens": 0, ...}

Root cause candidates:

• (a) Session JSONL serialization never writes per-turn usage records, so resume replay has nothing to count
• (b) Resume-mode stat accumulation reads memory-side live counters (always 0 since no API calls made in resume-only invocation)

Fix shape: persist usage records per turn into session JSONL; add total_usage summary block at tail; make /stats//cost in resume-mode sum persisted records; add regression test.

ROADMAP.md only diff: 1 file changed, 2 insertions(+)

Source: Jobdori live dogfood, e7074f4, 2026-04-29.