feat: Phase 2.5 - Variant Collections Spreadsheet Editor

Replaces JSON textarea with professional Excel-like spreadsheet interface for managing product variant properties.

Features:
- Handsontable 14.6.1 spreadsheet component
- Property presets (Size, Color, Material, Storage, Custom)
- Inline cell editing with Tab/Enter navigation
- Context menu for add/remove rows and columns
- Keyboard shortcuts (Ctrl+D delete, Ctrl+Enter save, Ctrl+Z undo)
- Mobile touch gestures (swipe to delete rows)
- Automatic JSON serialization on form submit
- Form validation before saving
- Comprehensive user guide documentation

Files Changed:
- LittleShop/package.json: NPM package management setup
- LittleShop/wwwroot/js/variant-editor.js: 400-line spreadsheet editor module
- LittleShop/wwwroot/lib/handsontable/: Handsontable library (Community Edition)
- LittleShop/wwwroot/lib/hammerjs/: Hammer.js touch gesture library
- LittleShop/Areas/Admin/Views/VariantCollections/Edit.cshtml: Spreadsheet UI integration
- VARIANT_COLLECTIONS_USER_GUIDE.md: Complete user guide (18+ pages)

Technical Details:
- Excel-like editing experience (no more manual JSON editing)
- Mobile-first responsive design
- Browser compatibility: Chrome 90+, Firefox 88+, Edge 90+, Safari 14+
- Touch-optimized for mobile administration
- Automatic data validation and error handling

LittleShop/wwwroot/lib/hammerjs/changelog.js

@@ -0,0 +1,71 @@
+var changelog = require( "changelogplease" );
+var gittags = require( "git-tags" ).get( function( error, tags ) {
+	if ( error ) {
+		throw error
+	}
+	console.log( tags[ 1 ] + ".." + tags[ 0 ] );
+	var exclude = [ "Merge", "Whitespace", "Fixup", "Cleanup", "Formatting", "Ignore" ];
+	changelog( {
+		ticketUrl: "https://github.com/hammerjs/hammer.js/issues/{id}",
+		commitUrl: "https://github.com/hammerjs/hammerjs/commit/{id}",
+		sort: false,
+		repo: "./",
+		committish: tags[ 1 ] + ".." + tags[ 0 ]
+	}, function( error, log ) {
+		if ( error ) {
+			throw error;
+		}
+		log = parseLog( log );
+		console.log( log );
+	} );
+	function parseLog( log ) {
+		var lines = log.split( "\n" );
+		var newLog = [];
+		var log = [];
+		var currentComponent;
+
+		
+		lines.shift();
+		lines.forEach( function( line ) {
+			var newLine = parseLine( line );
+			if ( newLine ) {
+				log.push( line );
+			}
+		} );
+		var log = log.join( "\n" );
+		return log.replace( /\*/g, "-" ).replace( /__TICKETREF__,/g, "" );
+	}
+	function parseLine( line ) {
+		var parts = getParts( line );
+
+		if ( exclude.indexOf( parts.component ) > -1 ) {
+			return false;
+		}
+		return parts;
+	}
+	function getParts( line ) {
+		var parts = line.split( ":" );
+		var component = "";
+		var message;
+		var commits = line.match( /\{\{([A-Za-z0-9 ]){0,99}\}\}/ )
+
+		if ( parts.length > 1 && parts[ 0 ].length <= 20 ) {
+			component = parts[ 0 ];
+			parts.shift();
+			message = parts.join( ":" );
+		} else {
+			parts = line.split( " " );
+			component = parts[ 1 ];
+			parts.shift();
+			message = parts.join( " " );
+		}
+
+		if ( component ) {
+			component = component.replace( /\* |,/, "" );
+		}
+		return {
+			component: component,
+			message: message
+		};
+	}
+} );