fix: resolve PHPCS errors and PHPUnit test failures for CI

Move declare(strict_types=1) after file-level docblock in all 12 class
files to satisfy WordPress Coding Standards docblock placement rule.
Fix multi-line function call formatting in class-psa-admin.php. Align
array double arrows and equals signs. Fix escaped backticks in
AIGeneratorTest heredoc that broke markdown fence stripping tests.

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

tests/unit/AIGeneratorTest.php

@@ -116,9 +116,9 @@ class AIGeneratorTest extends TestCase {
 	 */
 	public function test_parse_response_with_markdown_fences() {
 		$response_text = <<<JSON
-\`\`\`json
+```json
 {"is_valid": true, "canonical_name": "Semaglutide", "reason": "GLP-1 agonist"}
-\`\`\`
+```
 JSON;
 
 		$result = PSA_OpenRouter::parse_response( $response_text );