Add Quick Look Preview and Thumbnail extensions for .casera files

- Add CaseraQLPreview extension to show custom preview with contractor
  details and import instructions when viewing .casera files
- Add CaseraQLThumbnail extension to display teal icon in Messages
  and Files app instead of generic white box
- Update UTExportedTypeDeclarations to conform to public.content
  for better system file type recognition

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

iosApp/CaseraQLThumbnail/Info.plist

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>CFBundleDisplayName</key>
+	<string>Casera Thumbnail</string>
+	<key>CFBundleExecutable</key>
+	<string>$(EXECUTABLE_NAME)</string>
+	<key>CFBundleIdentifier</key>
+	<string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
+	<key>CFBundleInfoDictionaryVersion</key>
+	<string>6.0</string>
+	<key>CFBundleName</key>
+	<string>$(PRODUCT_NAME)</string>
+	<key>CFBundlePackageType</key>
+	<string>$(PRODUCT_BUNDLE_PACKAGE_TYPE)</string>
+	<key>CFBundleShortVersionString</key>
+	<string>1.0</string>
+	<key>CFBundleVersion</key>
+	<string>1</string>
+	<key>NSExtension</key>
+	<dict>
+		<key>NSExtensionAttributes</key>
+		<dict>
+			<key>QLSupportedContentTypes</key>
+			<array>
+				<string>com.casera.contractor</string>
+			</array>
+			<key>QLThumbnailMinimumDimension</key>
+			<integer>0</integer>
+		</dict>
+		<key>NSExtensionPrincipalClass</key>
+		<string>$(PRODUCT_MODULE_NAME).ThumbnailProvider</string>
+		<key>NSExtensionPointIdentifier</key>
+		<string>com.apple.quicklook.thumbnail</string>
+	</dict>
+</dict>
+</plist>

iosApp/CaseraQLThumbnail/ThumbnailProvider.swift

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+//
+//  ThumbnailProvider.swift
+//  CaseraQLThumbnail
+//
+//  Created by Trey Tartt on 12/6/25.
+//
+
+import UIKit
+import QuickLookThumbnailing
+
+class ThumbnailProvider: QLThumbnailProvider {
+
+    override func provideThumbnail(for request: QLFileThumbnailRequest, _ handler: @escaping (QLThumbnailReply?, Error?) -> Void) {
+
+        let thumbnailSize = request.maximumSize
+
+        handler(QLThumbnailReply(contextSize: thumbnailSize, currentContextDrawing: { () -> Bool in
+            // Draw background
+            let backgroundColor = UIColor(red: 7/255, green: 160/255, blue: 195/255, alpha: 1)
+            backgroundColor.setFill()
+            UIRectFill(CGRect(origin: .zero, size: thumbnailSize))
+
+            // Draw icon
+            let config = UIImage.SymbolConfiguration(pointSize: min(thumbnailSize.width, thumbnailSize.height) * 0.5, weight: .regular)
+            if let icon = UIImage(systemName: "person.crop.rectangle.stack", withConfiguration: config) {
+                let tintedIcon = icon.withTintColor(.white, renderingMode: .alwaysOriginal)
+                let iconSize = tintedIcon.size
+                let iconOrigin = CGPoint(
+                    x: (thumbnailSize.width - iconSize.width) / 2,
+                    y: (thumbnailSize.height - iconSize.height) / 2
+                )
+                tintedIcon.draw(at: iconOrigin)
+            }
+
+            return true
+        }), nil)
+    }
+}