Replace wall-clock import timeout with inactivity-based timeout
The Plaud sync subprocess timeout (600s wall-clock) was killing imports
that were actively transcribing. Now:
- Inner wait loop (cli.py) resets its inactivity timer on observe.status
events from sense.py, not just segment completions
- Inner segment_timeout restored to 600s (was bumped to 1200s as a
workaround)
- Outer subprocess timeout (plaud.py) raised to 3600s as a safety
backstop — the import CLI's own inactivity timeout handles normal cases