feat(design-system): add reusable Input primitive

ControlValueAccessor-based, standalone, OnPush. Sizes sm/md/lg, states default/error/success.
Colors/radius/spacing/transitions consumed via existing tenant CSS vars (--border-color,
--primary-color, --error-color, --success-color, etc) with fallbacks - compatible with
bootstrap JSON theming and Project Editor live preview.

src/app/shared/ui/input/input.component.html

@@ -0,0 +1,16 @@
+<input
+  class="app-input"
+  [class.app-input--sm]="size() === 'sm'"
+  [class.app-input--md]="size() === 'md'"
+  [class.app-input--lg]="size() === 'lg'"
+  [class.app-input--error]="state() === 'error'"
+  [class.app-input--success]="state() === 'success'"
+  [type]="type()"
+  [placeholder]="placeholder()"
+  [disabled]="isDisabled || disabled()"
+  [attr.aria-label]="ariaLabel()"
+  [attr.aria-invalid]="state() === 'error' || null"
+  [value]="value"
+  (input)="handleInput($event)"
+  (blur)="handleBlur()"
+/>