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

tests/bootstrap.php

@@ -209,6 +209,11 @@ if ( ! class_exists( 'WP_Post' ) ) {
 // Plugin URL and version constants used by admin enqueue methods.
 // Defined here so all tests that load admin classes can stub WP enqueue calls
 // without hitting "Undefined constant" errors.
+if ( ! defined( 'PRAUTOBLOGGER_DEFAULT_BOARD_COLUMN_LIMIT' ) ) {
+    define( 'PRAUTOBLOGGER_DEFAULT_BOARD_COLUMN_LIMIT', 20 );
+}
+
+// Plugin URL and version constants used by admin enqueue methods.
 if ( ! defined( 'PRAUTOBLOGGER_PLUGIN_URL' ) ) {
     define( 'PRAUTOBLOGGER_PLUGIN_URL', 'https://test.example.com/wp-content/plugins/prautoblogger/' );
 }