v0.5.2

Fixed

• p50 TTFT row missing from capture card: when the TTFT watchdog is
  enabled, updateUpstreamP50 writes p50 to SQLite but the WS
  "done"/"update" broadcast always carried upstream_ttft_p50_ms: null
  because buildSummary read from res.$upstream_ttft_p50_ms (never
  populated) instead of the DB. The dashboard's 4th row (p50 / tps /
  ratio) only appeared after a manual refresh. Fixed with a two-part
  approach: (1) flushNow now re-reads p50 from the DB via
  getUpstreamP50 and passes it to buildSummary as an override, so
  the done broadcast carries p50 when it's already in the DB; (2) the
  detached p50 .then() callback in proxy.ts emits a late WS
  "update" with summary(row) if the capture is already "done" —
  covering the case where p50 lands after the done broadcast. The
  overlap window (both fire) is idempotent and debounced client-side.