Merge Dev - streaming rate-limit, lineage cost reporting, v0.3.39

[aliroberts]

CLI: streaming rate-limit, lineage cost reporting, v0.3.39

Relay broadcast batching (per-session Realtime rate cap)

The weco start claude relay now coalesces transcript broadcasts and rate-limits them so a single streaming session can never exceed a fixed messages/sec ceiling on Supabase Realtime — independent of how fast the SDK emits.

• Lines that arrive within a flush window are batched into one transcript_batch event (array of lines) — coalesced, never dropped. Sparse output still sends immediately (no added latency); throttling only kicks in under load.
• Hard guarantee: ≤ 1000 / WECO_RELAY_FLUSH_MS msgs/sec per session (default 100ms → ≤10/s), env-tunable.
• Scrollback replay is batched the same way, so reconnect/takeover bursts also respect the cap. Oversized (>2.5MB) lines still fall back to transcript_chunk.
• ⚠️ Deploy ordering: the dashboard must understand transcript_batch before this CLI ships (the dashboard handler is backward-compatible — handles both old transcript and new transcript_batch). Ship dashboard first, then this.

Lineage-wide cost reporting

Run cost now reflects the entire lineage (parent + derived runs), not just the single run — check_run_cost queries the new /billing/run/{id}/lineage-cost endpoint (a superset of the per-run cost).

Version

Bump to 0.3.39.