Fix VHS quoting and make tape test runner Hide-aware

Sequential cleanup commands fixed the VHS parse error but exposed
a deeper issue: the test runner was blind to Hide/Show blocks,
so cleanup commands ran as tests and could delete jobs mid-sequence.

- test-tapes.sh now reads tapes line-by-line tracking Hide/Show state;
  only Type lines in visible (Show) blocks are executed as tests
- Pre-clean named jobs from each tape at start of run_tape to handle
  leftovers from previously failed runs (mirrors what the Hide cleanup
  does when VHS records the tape)
- 19 tape commands tested (cleanup commands correctly excluded)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

demo/all-features.tape

@@ -14,7 +14,7 @@ Sleep 1s
 
 # Clean up any pre-existing jobs with names used in this demo
 Hide
-Type "for n in healthcheck_home monitor_home backup_home health2_home; do systab -X \"$n\" 2>/dev/null || true; done"
+Type "systab -X healthcheck_home 2>/dev/null; systab -X monitor_home 2>/dev/null; systab -X backup_home 2>/dev/null; systab -X health2_home 2>/dev/null; true"
 Enter
 Sleep 1s
 Show