feat(web): implement complete workspace with themes, tabs, sidebar, and mobile

Transform CalcText from a single-document calculator into a full workspace
application with multi-document support, theming, and responsive mobile experience.

- Theme system: 5 presets (Light, Dark, Matrix, Midnight, Warm) + accent colors
- Document model with localStorage persistence and auto-save
- Tab bar with keyboard shortcuts (Ctrl+N/W/Tab/1-9), rename, close
- Sidebar with search, recent, favorites, folders, templates, drag-and-drop
- 5 templates: Budget, Invoice, Unit Converter, Trip Planner, Loan Calculator
- Status bar with cursor position, engine status, dedication to Igor Cassel
- Results panel: type-specific colors, click-to-copy, error hints
- Format toolbar: H, B, I, //, color labels with live preview toggle
- Syntax highlighting using theme CSS variables
- Error hover tooltips
- Mobile: bottom results tray, sidebar drawer, touch targets, safe areas
- Docker multi-stage build (Rust WASM + Vite + Nginx)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

calcpad-macos/Sources/CalcPad/Views/AnswerColumnView.swift

@@ -3,12 +3,13 @@ import SwiftUI
 
 /// Displays calculation results in a vertical column, one result per line,
 /// aligned to match the corresponding editor lines.
-/// Uses NSViewRepresentable wrapping NSScrollView + NSTextView for pixel-perfect
-/// line height alignment with the editor.
+/// Uses NSViewRepresentable wrapping NSScrollView + StripedTextView for
+/// pixel-perfect line height alignment with the editor, including zebra striping.
 struct AnswerColumnView: NSViewRepresentable {
     let results: [LineResult]
     @Binding var scrollOffset: CGFloat
     var font: NSFont
+    var alignment: NSTextAlignment = .right
 
     func makeCoordinator() -> Coordinator {
         Coordinator()
@@ -24,23 +25,23 @@ struct AnswerColumnView: NSViewRepresentable {
         scrollView.verticalScrollElasticity = .none
         scrollView.horizontalScrollElasticity = .none
 
-        let textView = NSTextView()
+        let textView = StripedTextView()
         textView.isEditable = false
         textView.isSelectable = true
         textView.isRichText = true
         textView.usesFontPanel = false
-        textView.drawsBackground = false
+        textView.drawsBackground = true
         textView.backgroundColor = .clear
 
         // Match editor text container settings for alignment
         textView.textContainer?.lineFragmentPadding = 4
         textView.textContainerInset = NSSize(width: 8, height: 8)
 
-        // Disable line wrapping to match editor behavior
-        textView.isHorizontallyResizable = true
-        textView.textContainer?.widthTracksTextView = false
+        // Let the text container track the scroll view width
+        textView.isHorizontallyResizable = false
+        textView.textContainer?.widthTracksTextView = true
         textView.textContainer?.containerSize = NSSize(
-            width: CGFloat.greatestFiniteMagnitude,
+            width: 0,
             height: CGFloat.greatestFiniteMagnitude
         )
         textView.maxSize = NSSize(
@@ -73,14 +74,15 @@ struct AnswerColumnView: NSViewRepresentable {
         let attributedString = NSMutableAttributedString()
 
         let paragraphStyle = NSMutableParagraphStyle()
-        paragraphStyle.alignment = .right
+        paragraphStyle.alignment = alignment
 
         let resultColor = NSColor.secondaryLabelColor
         let errorColor = NSColor.systemRed
 
         for (index, lineResult) in results.enumerated() {
-            let displayText = lineResult.result ?? ""
-            let color = lineResult.isError ? errorColor : resultColor
+            // Only show successful results — errors stay as underlines in the editor
+            let displayText = lineResult.isError ? "" : (lineResult.result ?? "")
+            let color = resultColor
 
             let attributes: [NSAttributedString.Key: Any] = [
                 .font: font,