docs: consolidate documentation into organized structure

- Move 12 markdown files from root to docs/ subdirectories
- Organize documentation by category:
  • docs/troubleshooting/ (1 file)  - Technical troubleshooting guides
  • docs/deployment/      (4 files) - Deployment and security documentation
  • docs/guides/          (3 files) - Feature-specific guides
  • docs/planning/        (4 files) - Planning and improvement proposals

Root directory cleanup:
- Reduced from 16 to 4 markdown files in root
- Only essential project files remain:
  • CLAUDE.md (AI instructions)
  • README.md (Main project readme)
  • CLEANUP_PLAN.md (Current cleanup plan)
  • SRC_STRUCTURE_IMPROVEMENTS.md (Structure improvements)

This improves:
✅ Documentation discoverability
✅ Logical organization by purpose
✅ Clean root directory
✅ Better maintainability

src/Application/Auth/LoginUser.php

@@ -4,7 +4,7 @@ declare(strict_types=1);
 
 namespace App\Application\Auth;
 
-class LoginUser
+final readonly class LoginUser
 {
     public function __construct(
         public string $email,

src/Application/Auth/LoginUserHandler.php

@@ -6,7 +6,7 @@ namespace App\Application\Auth;
 
 use App\Framework\CommandBus\CommandHandler;
 
-class LoginUserHandler
+final readonly class LoginUserHandler
 {
     #[CommandHandler]
     public function __invoke(LoginUser $loginUser): void

src/Application/Auth/ShowLogin.php

@@ -10,7 +10,7 @@ use App\Framework\CommandBus\CommandBus;
 use App\Framework\Http\Method;
 use App\Framework\Router\Result\ViewResult;
 
-class ShowLogin
+final readonly class ShowLogin
 {
     public function __construct(
         private CommandBus $commandBus,