feat: Integrate HTML templates with FastAPI

- Created template_helpers.py for centralized template rendering
- Added ux_features.css for enhanced UX styling
- Implemented JavaScript modules for:
  - Keyboard shortcuts (Ctrl+K, Ctrl+R navigation)
  - User preferences persistence
  - Undo/redo functionality (Ctrl+Z/Ctrl+Y)
  - Mobile responsive features
  - Touch gesture support
  - Accessibility features (ARIA, focus management)
  - Screen reader support
  - Color contrast compliance (WCAG)
  - Multi-screen support
- Updated page_controller.py and error_controller.py to use template helpers
- Created comprehensive template integration tests
- All templates verified: index.html, login.html, setup.html, queue.html, error.html
- Maintained responsive layout and theme switching
- Updated instructions.md (removed completed task)
- Updated infrastructure.md with template integration details

tests/unit/test_template_helpers.py

@@ -0,0 +1,86 @@
+"""
+Tests for template helper utilities.
+
+This module tests the template helper functions.
+"""
+from unittest.mock import Mock
+
+import pytest
+
+from src.server.utils.template_helpers import (
+    get_base_context,
+    list_available_templates,
+    validate_template_exists,
+)
+
+
+class TestTemplateHelpers:
+    """Test template helper utilities."""
+
+    def test_get_base_context(self):
+        """Test that base context is created correctly."""
+        request = Mock()
+        context = get_base_context(request, "Test Title")
+        
+        assert "request" in context
+        assert context["request"] == request
+        assert context["title"] == "Test Title"
+        assert context["app_name"] == "Aniworld Download Manager"
+        assert context["version"] == "1.0.0"
+
+    def test_get_base_context_default_title(self):
+        """Test that default title is used."""
+        request = Mock()
+        context = get_base_context(request)
+        
+        assert context["title"] == "Aniworld"
+
+    def test_validate_template_exists_true(self):
+        """Test template validation for existing template."""
+        # index.html should exist
+        exists = validate_template_exists("index.html")
+        assert exists is True
+
+    def test_validate_template_exists_false(self):
+        """Test template validation for non-existing template."""
+        exists = validate_template_exists("nonexistent.html")
+        assert exists is False
+
+    def test_list_available_templates(self):
+        """Test listing available templates."""
+        templates = list_available_templates()
+        
+        # Should be a list
+        assert isinstance(templates, list)
+        
+        # Should contain at least the main templates
+        expected_templates = [
+            "index.html",
+            "login.html",
+            "setup.html",
+            "queue.html",
+            "error.html"
+        ]
+        for expected in expected_templates:
+            assert expected in templates, (
+                f"{expected} not found in templates list"
+            )
+
+    def test_list_available_templates_only_html(self):
+        """Test that only HTML files are listed."""
+        templates = list_available_templates()
+        
+        for template in templates:
+            assert template.endswith(".html")
+
+    @pytest.mark.parametrize("template_name", [
+        "index.html",
+        "login.html",
+        "setup.html",
+        "queue.html",
+        "error.html"
+    ])
+    def test_all_required_templates_exist(self, template_name):
+        """Test that all required templates exist."""
+        assert validate_template_exists(template_name), \
+            f"Required template {template_name} does not exist"