feat: Implement default welcome page for missing web application

- Added a professional HTML welcome page displayed when no web application is configured.
- Enhanced `_load_webapp()` method to support improved path resolution for both development and bundled modes.
- Updated error handling to show the welcome page instead of a bare error message when the webapp file is not found.
- Modified unit tests to verify the welcome page is displayed in error scenarios.

build: Complete Windows and macOS build scripts

- Created `build_windows.py` for building Windows executable and optional MSI installer using PyInstaller.
- Developed `build_macos.sh` for creating macOS application bundle and DMG image.
- Added logging and error handling to build scripts for better user feedback.

docs: Add build and icon requirements documentation

- Created `PHASE_3_BUILD_SUMMARY.md` detailing the build process, results, and next steps.
- Added `resources/icons/README.md` outlining icon requirements and creation guidelines.

chore: Sync remotes script for repository maintenance

- Introduced `sync_remotes.ps1` PowerShell script to fetch updates from origin and upstream remotes.

build/scripts/sync_remotes.ps1

@@ -0,0 +1,55 @@
+# Sync script to keep origin and upstream remotes in sync
+# Usage: .\sync_remotes.ps1 [--push-to-origin]
+
+param(
+    [switch]$PushToOrigin
+)
+
+$ErrorActionPreference = "Stop"
+$scriptPath = Split-Path -Parent $MyInvocation.MyCommand.Path
+$repoRoot = Split-Path -Parent (Split-Path -Parent $scriptPath)
+
+Write-Host "🔄 WebDrop Bridge - Remote Sync Script" -ForegroundColor Cyan
+Write-Host "Repository: $repoRoot`n" -ForegroundColor Gray
+
+# Change to repo directory
+Push-Location $repoRoot
+
+try {
+    # Fetch from both remotes
+    Write-Host "📥 Fetching from origin..." -ForegroundColor Yellow
+    git fetch origin
+    
+    Write-Host "📥 Fetching from upstream..." -ForegroundColor Yellow
+    git fetch upstream
+    
+    # Show status
+    Write-Host "`n📊 Remote Status:" -ForegroundColor Cyan
+    git remote -v
+    
+    # Show branch comparison
+    Write-Host "`n📋 Branch Comparison:" -ForegroundColor Cyan
+    Write-Host "Local branches vs origin:" -ForegroundColor Gray
+    git log --oneline origin/main -5 | ForEach-Object { Write-Host "  origin: $_" }
+    Write-Host ""
+    git log --oneline upstream/main -5 | ForEach-Object { Write-Host "  upstream: $_" }
+    
+    # Optionally push to origin
+    if ($PushToOrigin) {
+        Write-Host "`n📤 Pushing current branch to origin..." -ForegroundColor Yellow
+        $currentBranch = git rev-parse --abbrev-ref HEAD
+        git push origin $currentBranch
+        Write-Host "✅ Pushed $currentBranch to origin" -ForegroundColor Green
+    } else {
+        Write-Host "`n💡 Tip: Use --push-to-origin flag to push current branch to origin" -ForegroundColor Gray
+    }
+    
+    Write-Host "`n✅ Sync complete!" -ForegroundColor Green
+}
+catch {
+    Write-Host "`n❌ Error: $_" -ForegroundColor Red
+    exit 1
+}
+finally {
+    Pop-Location
+}