Fix "in N minutes" parsing and VHS tape errors

- Strip "in " prefix before passing to date -d (was always broken)
- Fix quickstart tape: -B3 → -B4 for resume grep (Job: is 4 lines back)
- Fix notifications tape: -f ~/backup.sh → -c (file doesn't exist)

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

demo/quickstart.tape

@@ -0,0 +1,62 @@
+# systab — Quick Start
+# Creates a few jobs, checks status, views logs, then cleans up.
+
+Output demo/quickstart.gif
+Set Shell bash
+Set Width 1200
+Set Height 600
+Set FontSize 16
+
+Set TypingSpeed 50ms
+
+Sleep 1s
+
+# Create a recurring job
+Type "systab -t 'every 5 minutes' -c 'echo health check OK'"
+Sleep 500ms
+Enter
+Sleep 2s
+
+# Create a one-time job
+Type "systab -t 'in 30 minutes' -c 'echo reminder: meeting soon'"
+Sleep 500ms
+Enter
+Sleep 2s
+
+# Check status of all jobs
+Type "systab -S"
+Sleep 500ms
+Enter
+Sleep 4s
+
+# View logs
+Type "systab -L"
+Sleep 500ms
+Enter
+Sleep 3s
+
+# Pause a job (uses the first job ID from status)
+Type "systab -P $(systab -S 2>/dev/null | grep -m1 'Job:' | awk '{print $2}')"
+Sleep 500ms
+Enter
+Sleep 2s
+
+# Show it's paused
+Type "systab -S"
+Sleep 500ms
+Enter
+Sleep 3s
+
+# Resume it
+Type "systab -R $(systab -S 2>/dev/null | grep -m1 'Disabled' -B4 | grep 'Job:' | awk '{print $2}')"
+Sleep 500ms
+Enter
+Sleep 2s
+
+# Clean up completed one-time jobs
+Type "systab -C"
+Sleep 500ms
+Enter
+Sleep 2s
+
+Sleep 2s