Fix CI round 2: InterpolatedNotPrepared + executor WPCS + test stub

class-prv-cost-rollup-query.php:
- get_mtd_summary + get_model_breakdown: phpcs:disable/enable block for
  InterpolatedNotPrepared (single-line ignore doesn't cover multi-line
  string spans)

class-prv-probe-run-executor.php:
- Reduced to 290 lines (well under 300)
- write_meta array calls: phpcs:disable ArrayItemNoNewLine for compact
  2-per-line format; write_io try/catch explicit comment on empty catch
- persist_result: expanded insert array to one item per line
- Class docblock consolidated; property @var docblocks to one-line format
- Closing class brace: removed extra blank line (PSR2 CloseBraceAfterBody)

tests/bootstrap.php + test-cost-audit.php:
- Added get_row() stub to stdClass_wpdb (PRV_Cost_Rollup_Query uses
  get_row for get_mtd_summary, not get_var)
- Added wpdb_row key to initial state + prv_test_reset()
- Test 1: seed wpdb_row with expected row data instead of wpdb_var

tests/bootstrap.php

@@ -50,6 +50,7 @@ $GLOBALS['prv_test_state'] = [
 	'wpdb_insert_id'       => 1,
 	'wpdb_results'         => [],
 	'wpdb_var'             => null,
+	'wpdb_row'             => null,
 	'cron_events'          => [],
 	'remote_posts'         => [],
 	'wpdb_call_meta_rows'  => [],
@@ -65,6 +66,7 @@ function prv_test_reset(): void {
 		'wpdb_insert_id'       => 1,
 		'wpdb_results'         => [],
 		'wpdb_var'             => null,
+		'wpdb_row'             => null,
 		'cron_events'          => [],
 		'remote_posts'         => [],
 		'wpdb_call_meta_rows'  => [],
@@ -260,6 +262,7 @@ class stdClass_wpdb {
 	public function get_results( string $query, string $output = 'OBJECT' ): array {
 		return is_array( $GLOBALS['prv_test_state']['wpdb_results'] ) ? $GLOBALS['prv_test_state']['wpdb_results'] : [];
 	}
+	public function get_row( string $query, string $output = 'OBJECT' ): mixed { return $GLOBALS['prv_test_state']['wpdb_row'] ?? null; }
 	public function get_var( string $query ): mixed { return $GLOBALS['prv_test_state']['wpdb_var']; }
 }