feat: complete Phase 4 UI Components planning and issue creation (#73)

feat: phase 4 UI components planning and design tokens (#73)

## Phase 4 Documentation
- Created comprehensive issue templates for all 19 UI components
- Documented implementation timeline and dependencies
- Added issue tracking with actual GitHub issue numbers
- Updated TODO.md with issue links

## Design Tokens Implementation (#57)
- Added comprehensive design token system to app/globals.css
- Created TypeScript interface for type-safe token access
- Documented all tokens with usage examples
- Implemented spacing scale, typography, breakpoints, and utilities

This PR establishes the foundation for Phase 4 UI component development with proper planning documentation and a robust design token system.

Author: nullcoder

app/globals.css

@@ -4,6 +4,62 @@
 @custom-variant dark (&:is(.dark *));
 
 @theme inline {
+  /* Spacing Scale */
+  --spacing-0: 0;
+  --spacing-1: 0.25rem; /* 4px */
+  --spacing-2: 0.5rem; /* 8px */
+  --spacing-3: 0.75rem; /* 12px */
+  --spacing-4: 1rem; /* 16px */
+  --spacing-5: 1.25rem; /* 20px */
+  --spacing-6: 1.5rem; /* 24px */
+  --spacing-8: 2rem; /* 32px */
+  --spacing-10: 2.5rem; /* 40px */
+  --spacing-12: 3rem; /* 48px */
+  --spacing-16: 4rem; /* 64px */
+  --spacing-20: 5rem; /* 80px */
+  --spacing-24: 6rem; /* 96px */
+
+  /* Typography Scale */
+  --font-size-xs: 0.75rem; /* 12px */
+  --font-size-sm: 0.875rem; /* 14px */
+  --font-size-base: 1rem; /* 16px */
+  --font-size-lg: 1.125rem; /* 18px */
+  --font-size-xl: 1.25rem; /* 20px */
+  --font-size-2xl: 1.5rem; /* 24px */
+  --font-size-3xl: 1.875rem; /* 30px */
+  --font-size-4xl: 2.25rem; /* 36px */
+  --font-size-5xl: 3rem; /* 48px */
+  --font-size-6xl: 3.75rem; /* 60px */
+
+  /* Line Heights */
+  --leading-none: 1;
+  --leading-tight: 1.25;
+  --leading-snug: 1.375;
+  --leading-normal: 1.5;
+  --leading-relaxed: 1.625;
+  --leading-loose: 2;
+
+  /* Font Weights */
+  --font-weight-normal: 400;
+  --font-weight-medium: 500;
+  --font-weight-semibold: 600;
+  --font-weight-bold: 700;
+
+  /* Breakpoints */
+  --breakpoint-sm: 640px;
+  --breakpoint-md: 768px;
+  --breakpoint-lg: 1024px;
+  --breakpoint-xl: 1280px;
+  --breakpoint-2xl: 1536px;
+
+  /* Container Max Widths */
+  --container-sm: 640px;
+  --container-md: 768px;
+  --container-lg: 1024px;
+  --container-xl: 1280px;
+  --container-2xl: 1536px;
+
+  /* Colors */
   --color-background: var(--background);
   --color-foreground: var(--foreground);
   --font-sans: var(--font-geist-sans);
@@ -37,10 +93,32 @@
   --color-popover: var(--popover);
   --color-card-foreground: var(--card-foreground);
   --color-card: var(--card);
+
+  /* Border Radius */
   --radius-sm: calc(var(--radius) - 4px);
   --radius-md: calc(var(--radius) - 2px);
   --radius-lg: var(--radius);
   --radius-xl: calc(var(--radius) + 4px);
+
+  /* Shadows */
+  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
+  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
+  --shadow-lg:
+    0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
+  --shadow-xl:
+    0 20px 25px -5px rgb(0 0 0 / 0.1), 0 8px 10px -6px rgb(0 0 0 / 0.1);
+
+  /* Animation Durations */
+  --duration-fast: 150ms;
+  --duration-normal: 300ms;
+  --duration-slow: 500ms;
+
+  /* Z-Index Scale */
+  --z-index-10: 10;
+  --z-index-20: 20;
+  --z-index-30: 30;
+  --z-index-40: 40;
+  --z-index-50: 50;
 }
 
 :root {