feat: implement HTMX base templates and partials

[pythoninthegrass]

Summary

Implement foundational HTMX templates and partials for the MusicBee-inspired music player interface.

Changes

🎨 Three-Panel Layout

• Main application template with left sidebar, center content, and right queue panels
• Responsive design that adapts to different screen sizes
• Proper flexbox layout for optimal space utilization

🔧 Core Dependencies

• HTMX 1.9.10 with WebSocket and Server-Sent Events support
• Alpine.js 3.13.5 for reactive UI components
• Tailwind CSS with Basecoat UI design system
• Inter font for modern typography
• Bootstrap Icons for consistent iconography

🧩 Reusable Components

• Navbar: Search functionality, theme toggle, user menu
• Sidebar: Library navigation, playlist management, statistics
• Player Controls: Full-featured audio controls with progress bar and volume
• Queue: Interactive queue with drag-and-drop reordering
• Modal: Flexible modal system for dialogs and forms
• Toast: Non-intrusive notification system
• Track Item: Consistent track display component

🎯 Template System

• Proper Jinja2 template inheritance structure
• Modular component design for maintainability
• Template filters for duration and file size formatting
• Comprehensive documentation

🎨 Design System

• MusicBee-inspired dark theme
• Consistent color palette and spacing
• Smooth animations and transitions
• Keyboard shortcuts and accessibility features

📱 Frontend JavaScript

• HTMX integration utilities
• Keyboard shortcut handling
• Toast and modal management
• Drag-and-drop functionality
• Theme management

Files Added

• templates/base/base.html - Main application layout
• templates/components/ - Reusable UI components
• templates/partials/ - Modal, toast, and track item partials
• templates/pages/library.html - Example page implementation
• static/js/app.js - Frontend JavaScript utilities
• static/css/main.css - Enhanced with Basecoat UI
• templates/README.md - Comprehensive documentation

Closes

• Task 026: Create HTMX base templates and partials

Testing

• Template inheritance and component rendering
• Responsive layout across different screen sizes
• HTMX dynamic content loading
• Alpine.js reactive components
• Keyboard shortcuts functionality