feat(worker): surface memory stats in run log and fix log-level colors

[albanm]

Make the per-task memory debug logs added in #90 actually useful in the
run log UI, and fix two stale color choices in the run-log component.

Why: the new memory-reporter was pushing debug('memory', formatMem(...))
into run.log, but run-logs-list.vue only renders log.msg — the
actual rss=… heapUsed=… … payload (stored in extra) was silently
dropped. There were also no startup / exit entries to anchor the
periodic samples in time.

What changed:

• worker/src/task/memory-reporter.ts — when processing.debug, emit a
  unified Task process memory stats - rss=… heapTotal=… heapUsed=… …
  debug entry at startup, on every sample interval, and at stop. Payload
  is now in msg (visible in the UI) rather than extra.
• worker/src/task/task.ts — capture the reporter handle and
  await memReporter.stop() in finally, so the closing entry lands
  after the final success/error log.
• ui/src/components/run/run-logs-list.vue — warning entries now use
  text-warning (were text-info), and debug entries use
  text-medium-emphasis so they're visually distinct from info.

Regression risks:

• The run-log color change applies to every existing warning /
  debug entry across all runs, not only the new memory lines.
• MemoryReporterHandle.stop() is now async; the single in-tree caller
  was updated to await it.
• The exit memory entry is pushed via log.debug (mongo write + ws
  emit). If mongo stalls on shutdown, the task child waits on it — same
  pattern as the existing final success/error log.