feat(ai): generate AGENTS.md in ai:generate-instructions command

Also write project AI instructions to AGENTS.md alongside the existing
copilot, cursor, gemini, and windsurf output files.

flight/commands/AiGenerateInstructionsCommand.php

@@ -167,7 +167,7 @@ class AiGenerateInstructionsCommand extends AbstractBaseCommand
         $io->info(
             'Updating .github/copilot-instructions.md, '
                 . '.cursor/rules/project-overview.mdc, '
-                . '.gemini/GEMINI.md and .windsurfrules...',
+                . '.gemini/GEMINI.md, .windsurfrules and AGENTS.md...',
             true
         );
 
@@ -184,6 +184,7 @@ class AiGenerateInstructionsCommand extends AbstractBaseCommand
         file_put_contents($this->projectRoot . '.cursor/rules/project-overview.mdc', $instructions);
         file_put_contents($this->projectRoot . '.gemini/GEMINI.md', $instructions);
         file_put_contents($this->projectRoot . '.windsurfrules', $instructions);
+        file_put_contents($this->projectRoot . 'AGENTS.md', $instructions);
         $io->ok('AI instructions updated successfully.', true);
         return 0;
     }

tests/commands/AiGenerateInstructionsCommandTest.php

@@ -167,6 +167,7 @@ class AiGenerateInstructionsCommandTest extends TestCase
         $this->assertFileExists($this->baseDir . '.cursor/rules/project-overview.mdc');
         $this->assertFileExists($this->baseDir . '.gemini/GEMINI.md');
         $this->assertFileExists($this->baseDir . '.windsurfrules');
+        $this->assertFileExists($this->baseDir . 'AGENTS.md');
     }
 
     public function testNoInstructionsReturnedFromLlm()