feat: M4 in-admin manual generation on chained-cron checkpoints + IA/perf pass (v0.21.0) (#166)

Final Phase 2 admin milestone. Board "New Article" runs through the M3 chained-cron checkpoint state machine (one stage/idea per tick, queue persisted before generate, lock released on every exit path) so generation survives Hostinger background-kill; retires the SSH-only do_action workaround (WP-CLI routes through the same entry). IA/perf: settings-backed board/ideas pagination + db 1.4.0 indexes. Folds guard P2s (--self-test + window doc).

QA: APPROVE-WITH-P2-NOTES @ f2a00d4 + delta APPROVE @ 0c8071f. Deferred (tracked): class-admin-page.php 353-line split + pagination Settings-UI fields.

Agent-Session: phase2-admin-m4-20260614

includes/admin/class-board-gen-log-query.php

@@ -76,8 +76,9 @@ class PRAutoBlogger_Board_Gen_Log_Query {
 				  AND post_id IS NULL
 				GROUP BY run_id
 				ORDER BY started_at DESC
-				LIMIT 10",
-				$since
+				LIMIT %d",
+				$since,
+				(int) max( 5, get_option( 'prautoblogger_board_column_limit', PRAUTOBLOGGER_DEFAULT_BOARD_COLUMN_LIMIT ) )
 			),
 			ARRAY_A
 		);
@@ -148,8 +149,9 @@ class PRAutoBlogger_Board_Gen_Log_Query {
 				  AND post_id IS NULL
 				GROUP BY run_id
 				ORDER BY started_at DESC
-				LIMIT 20",
-				$since
+				LIMIT %d",
+				$since,
+				(int) max( 5, get_option( 'prautoblogger_board_column_limit', PRAUTOBLOGGER_DEFAULT_BOARD_COLUMN_LIMIT ) )
 			),
 			ARRAY_A
 		);