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/App/CalcPadApp.swift

@@ -1,10 +1,20 @@
+import AppKit
 import SwiftUI
 
 @main
 struct CalcPadApp: App {
+    init() {
+        // Without a .app bundle, macOS treats the process as a background app
+        // that cannot receive keyboard input. This makes it a regular foreground app.
+        NSApplication.shared.setActivationPolicy(.regular)
+    }
+
     var body: some Scene {
         WindowGroup {
             ContentView()
+                .onAppear {
+                    NSApplication.shared.activate(ignoringOtherApps: true)
+                }
         }
         .defaultSize(width: 800, height: 600)
     }