refactor: consolidate utilities, clean up components, and improve theme persistence

- Consolidate common utilities (cn, format, time) into lib/utils
- Remove redundant utility files from pastel and units directories
- Clean up unused components (Separator, KeyboardShortcutsHelp)
- Relocate CommandPalette to components/units/ui/
- Force dark mode on landing page and improve theme persistence logic
- Add FOUC prevention script to RootLayout
- Fix sidebar height constraint in AppShell

lib/utils/format.ts

@@ -0,0 +1,54 @@
+/**
+ * Format a number for display with proper precision
+ */
+export function formatNumber(
+  value: number,
+  options: {
+    maxDecimals?: number;
+    minDecimals?: number;
+    notation?: 'standard' | 'scientific' | 'engineering' | 'compact';
+  } = {}
+): string {
+  const {
+    maxDecimals = 6,
+    minDecimals = 0,
+    notation = 'standard',
+  } = options;
+
+  // Handle edge cases
+  if (!isFinite(value)) return value.toString();
+  if (value === 0) return '0';
+
+  // Use scientific notation for very large or very small numbers
+  const absValue = Math.abs(value);
+  const useScientific =
+    notation === 'scientific' ||
+    (notation === 'standard' && (absValue >= 1e10 || absValue < 1e-6));
+
+  if (useScientific) {
+    return value.toExponential(maxDecimals);
+  }
+
+  // Format with appropriate decimal places
+  const formatted = new Intl.NumberFormat('en-US', {
+    minimumFractionDigits: minDecimals,
+    maximumFractionDigits: maxDecimals,
+    notation: notation === 'compact' ? 'compact' : 'standard',
+  }).format(value);
+
+  return formatted;
+}
+
+/**
+ * Parse a number input string
+ */
+export function parseNumberInput(input: string): number | null {
+  if (!input || input.trim() === '') return null;
+
+  // Remove spaces and replace comma with dot
+  const cleaned = input.replace(/\s/g, '').replace(',', '.');
+
+  const parsed = parseFloat(cleaned);
+
+  return isNaN(parsed) ? null : parsed;
+}