Code quality improvements from code review

- Add admin-only authorization for company and projects CRUD operations
- Create requireAccountId middleware to eliminate code duplication
- Standardize error handling (use next(error) consistently)
- Change error messages to Slovak language

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/controllers/admin.controller.js

@@ -54,7 +54,7 @@ export const createUser = async (req, res, next) => {
         : 'Používateľ úspešne vytvorený. Email môže byť nastavený neskôr.',
     });
   } catch (error) {
-    return next(error);
+    next(error);
   }
 };
 
@@ -72,7 +72,7 @@ export const getAllUsers = async (req, res, next) => {
       data: allUsers,
     });
   } catch (error) {
-    return next(error);
+    next(error);
   }
 };
 
@@ -93,7 +93,7 @@ export const getUser = async (req, res, next) => {
       },
     });
   } catch (error) {
-    return next(error);
+    next(error);
   }
 };
 
@@ -120,7 +120,7 @@ export const changeUserRole = async (req, res, next) => {
       message: 'Rola používateľa bola zmenená',
     });
   } catch (error) {
-    return next(error);
+    next(error);
   }
 };
 
@@ -140,7 +140,7 @@ export const deleteUser = async (req, res, next) => {
       deletedEmailAccounts: result.deletedEmailAccounts,
     });
   } catch (error) {
-    return next(error);
+    next(error);
   }
 };
 
@@ -157,6 +157,6 @@ export const getServerStatus = async (req, res, next) => {
       data: status,
     });
   } catch (error) {
-    return next(error);
+    next(error);
   }
 };