Fix enabled-sources checkbox not persisting when all unchecked

Browser omits checkbox fields from POST when none are checked, so the
prautoblogger_enabled_sources option retained its previous value (with
Reddit). Added a hidden input to the checkboxes renderer so an empty
value is always submitted. Also replaced the hardcoded "Collecting
sources from Reddit…" pipeline status with a dynamic message reflecting
actually-enabled sources.

Bump 0.6.2 → 0.6.3.

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

includes/admin/class-admin-page.php

@@ -158,6 +158,11 @@ class PRAutoBlogger_Admin_Page {
 
 			case 'checkboxes':
 				$current = json_decode( (string) $value, true ) ?: [];
+				// Hidden input ensures an empty value is POSTed when all boxes
+				// are unchecked — without this, the browser omits the field
+				// entirely, so WordPress never fires the sanitize callback and
+				// the old value persists in wp_options.
+				printf( '<input type="hidden" name="%s" value="" />', $id );
 				foreach ( ( $args['options'] ?? [] ) as $v => $label ) {
 					$is_checked = in_array( $v, $current, true );
 					$disabled   = strpos( $label, 'coming soon' ) !== false ? ' disabled' : '';