Refactor: deduplicate notifications, fix timer parsing, -o optional arg

- Extract build_job_list helper (shared by show_status/list_logs)
- clean_jobs now calls remove_job instead of inline stop/disable/rm
- Extract status preamble in write_notify_lines (icon_pre/status_pre)
- Replace fragile list-timers tail/awk with systemctl show properties
- Combine consecutive sed -i calls into single invocations
- Simplify is_manage_mode check to use existing manage_count
- Make -o accept optional line count arg (-o 20 or just -o for default 10)
- Fix %%s escaping in unit files and document in CLAUDE.md

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

README.md

@@ -75,7 +75,7 @@ systab -t "in 1 hour" -c "make build" -i
 systab -t "every day at 6am" -c "df -h" -m user@example.com
 
 # Include last 10 lines of output in notification
-systab -t "every day at 6am" -c "df -h" -i -o 10
+systab -t "every day at 6am" -c "df -h" -i -o
 ```
 
 ### Managing jobs
@@ -145,7 +145,7 @@ Job Creation:
   -f <script>       Script file to execute (reads stdin if neither -c nor -f)
   -i                Send desktop notification on completion (success/failure)
   -m <email>        Send email notification to address (via sendmail)
-  -o <lines>        Include last N lines of job output in notifications (default: 10)
+  -o [lines]        Include job output in notifications (default: 10 lines)
 
 Management:
   -P <id>           Pause (disable) a job