fix: QA remediation P1-A/P1-B/P1-C/P2 for v0.22.1 sync-mode

P1-A: wrap wp_schedule_single_event(GENERATE_ACTION) + fire_cron_now() in
on_orchestrate_tick() with 'if ( ! self::$sync_mode )' guard.
Mirrors the existing guard in on_generate_tick(). Prevents a background
wp-cron process spawning in parallel with the VPS --sync loop and
prematurely finalizing the run lock before Article_Worker completes.

P1-B: add two unit tests to GenerationCheckpointRunnerTest.php:
- test_orchestrate_tick_in_sync_mode_does_not_schedule_background_event:
  asserts sync_mode=true suppresses GENERATE_ACTION schedule + spawn_cron.
- test_generate_tick_async_mode_schedules_generate_action:
  asserts sync_mode=false (async path) still reschedules GENERATE_ACTION.

P1-C: create root CONTEXT.md with domain glossary (run, run_stages,
checkpoint, idea queue, Generation_Lock) and execution mode reference
(async wp-cron vs --sync VPS-driven).

P2: update ARCHITECTURE.md §25 Entry Points table with the
'wp prautoblogger generate --sync' VPS path row.

Agent-Session: prab-reliability-remediation-20260622

includes/core/class-generation-checkpoint-runner.php

@@ -175,10 +175,15 @@ class PRAutoBlogger_Generation_Checkpoint_Runner {
 				)
 			);
 
-			if ( ! wp_next_scheduled( self::GENERATE_ACTION ) ) {
-				wp_schedule_single_event( time(), self::GENERATE_ACTION );
+			// In sync mode the VPS tick loop is the external driver; skip
+			// wp-cron reschedule to prevent a competing background tick.
+			// on_generate_tick() has the same guard for subsequent reschedules.
+			if ( ! self::$sync_mode ) {
+				if ( ! wp_next_scheduled( self::GENERATE_ACTION ) ) {
+					wp_schedule_single_event( time(), self::GENERATE_ACTION );
+				}
+				PRAutoBlogger_Generation_Checkpoint_Helpers::fire_cron_now();
 			}
-			PRAutoBlogger_Generation_Checkpoint_Helpers::fire_cron_now();
 
 		} catch ( \Throwable $e ) {
 			PRAutoBlogger_Logger::instance()->error(