feat: Implement user authentication and database migration system

- Refactored AuthService to use UserRepository for user authentication.
- Added .env file for environment configuration.
- Created migration system with Migrator and ConnectionFactory classes.
- Added database migration files for creating users table.
- Implemented settings controller for managing database migrations.
- Developed user repository for user data handling.
- Created users controller for user management interface.
- Added frontend standards and migration documentation.
- Introduced reusable UI components and jQuery alerts module.

resources/scss/login.scss

@@ -1,14 +1,6 @@
+@use "shared/ui-components";
+
 :root {
-  --c-primary: #6690f4;
-  --c-primary-dark: #3164db;
-  --c-bg: #f4f6f9;
-  --c-surface: #ffffff;
-  --c-text: #4e5e6a;
-  --c-text-strong: #2d3748;
-  --c-border: #e2e8f0;
-  --c-muted: #718096;
-  --c-danger: #cc0000;
-  --focus-ring: 0 0 0 3px rgba(102, 144, 244, 0.15);
   --shadow-card: 0 20px 50px rgba(22, 34, 58, 0.14);
 }
 
@@ -105,18 +97,11 @@ h1 {
   color: var(--c-muted);
 }
 
-.alert-error {
+.login-alert {
   margin-bottom: 18px;
-  padding: 12px 14px;
-  border-radius: 8px;
-  border: 1px solid #fed7d7;
-  background: #fff5f5;
-  color: var(--c-danger);
-  font-size: 13px;
-  min-height: 44px;
 }
 
-.alert-error-placeholder {
+.login-alert-placeholder {
   opacity: 0.56;
 }
 
@@ -136,56 +121,20 @@ h1 {
   font-weight: 600;
 }
 
-input[type="email"],
-input[type="password"] {
-  width: 100%;
-  height: 46px;
-  border: 2px solid var(--c-border);
-  border-radius: 8px;
+.login-form .form-control {
+  min-height: 46px;
   padding: 0 14px;
-  font: inherit;
-  color: var(--c-text-strong);
-  background: #ffffff;
-  transition: border-color 0.2s ease, box-shadow 0.2s ease;
+  border-width: 2px;
 }
 
-input[type="email"]::placeholder,
-input[type="password"]::placeholder {
+.login-form .form-control::placeholder {
   color: #cbd5e0;
 }
 
-input[type="email"]:focus,
-input[type="password"]:focus {
-  outline: none;
-  border-color: var(--c-primary);
-  box-shadow: var(--focus-ring);
-}
-
-.submit-btn {
+.login-submit {
   margin-top: 2px;
-  height: 48px;
-  border: 0;
-  border-radius: 8px;
-  font: inherit;
   font-size: 15px;
-  font-weight: 600;
-  color: #ffffff;
-  background: var(--c-primary);
-  cursor: pointer;
-  transition: background-color 0.2s ease, transform 0.1s ease;
-}
-
-.submit-btn:hover {
-  background: var(--c-primary-dark);
-}
-
-.submit-btn:active {
-  transform: translateY(1px);
-}
-
-.submit-btn:focus-visible {
-  outline: none;
-  box-shadow: var(--focus-ring);
+  min-height: 48px;
 }
 
 @keyframes card-enter {