chore(psr4): phase 3 (Core) — namespace Core/Enum + Core/Exception

- Core/Enum → XcVm\Core\Enum (BootContext, ModuleState, ServerEnvironment).
- Core/Exception → XcVm\Core\Exception (XcVmException) + \Container
  (ContainerException, CircularDependencyException, ServiceCreationException) +
  \Module (ModuleException + the 4 module exceptions). The hierarchy resolves:
  XcVmException extends \RuntimeException; the Container/Module exceptions extend
  XcVmException via use; ContainerException keeps its PSR ContainerExceptionInterface.
- Add use to referrers across src/ and tests/; fix the leading-backslash refs
  qualified in earlier hub commits (\ModuleState, \ServerEnvironment,
  \XcVmException, \ContainerException, \ModuleLoadException, ...) to their FQCNs.
- phpstan-baseline.neon regenerated (292→292).

Verified: php -l clean; PHPStan no errors (first pass); PHPUnit 295/295;
leading-backslash re-sweep clean.

src/Core/Exception/Module/ModuleCycleException.php

@@ -1,5 +1,7 @@
 <?php
 
+namespace XcVm\Core\Exception\Module;
+
 use XcVm\Core\Module\ModuleLoader;
 /**
  * Thrown when ModuleLoader detects a circular dependency between modules.

src/Core/Exception/Module/ModuleException.php

@@ -1,5 +1,8 @@
 <?php
 
+namespace XcVm\Core\Exception\Module;
+use XcVm\Core\Exception\XcVmException;
+
 /**
  * Base exception for module lifecycle errors.
  *

src/Core/Exception/Module/ModuleLoadException.php

@@ -1,5 +1,7 @@
 <?php
 
+namespace XcVm\Core\Exception\Module;
+
 /**
  * Thrown when a module class cannot be instantiated or registered.
  *

src/Core/Exception/Module/ModuleManifestException.php

@@ -1,5 +1,7 @@
 <?php
 
+namespace XcVm\Core\Exception\Module;
+
 /**
  * Thrown when a module.json manifest is invalid, malformed, or missing required fields.
  *

src/Core/Exception/Module/ModuleNotFoundException.php

@@ -1,5 +1,7 @@
 <?php
 
+namespace XcVm\Core\Exception\Module;
+
 /**
  * Thrown when a requested module or its dependency cannot be found.
  *