Implement create operations for board, lane, and card

createBoard fills or mints a .kanban (or extension-less) folder and
refuses to clobber an existing board; createLane/createCard mint fresh
lowercase-UUIDv4 folders and append at max+1024 among visible siblings
via the same strict scan renumber uses (extracted, shared). New files
carry schema/title?/order?/created/modified — created==modified, no
modified-by — written LF through the same atomic temp+rename path.
The editability pre-flight is now scoped to operations that rewrite
siblings: renumber refuses on an uneditable sibling, a create beside
one proceeds. Schema constant unified on BoardLoader.supportedSchema.
Info.plist declares the .kanban document type (UTI conforming to
com.apple.package) so Finder treats a board as one document.

20 new unit tests; 196 total green.

Claude-Session: https://claude.ai/code/session_018BjQRYBR6jQja3jCRi5S3A

Kanban/Info.plist

@@ -26,5 +26,39 @@
 	<string>© 2026 rzen</string>
 	<key>NSPrincipalClass</key>
 	<string>NSApplication</string>
+	<key>UTExportedTypeDeclarations</key>
+	<array>
+		<dict>
+			<key>UTTypeIdentifier</key>
+			<string>dev.rzen.indie.kanban-board</string>
+			<key>UTTypeConformsTo</key>
+			<array>
+				<string>com.apple.package</string>
+				<string>public.directory</string>
+			</array>
+			<key>UTTypeDescription</key>
+			<string>Lanework Board</string>
+			<key>UTTypeTagSpecification</key>
+			<dict>
+				<key>public.filename-extension</key>
+				<string>kanban</string>
+			</dict>
+		</dict>
+	</array>
+	<key>CFBundleDocumentTypes</key>
+	<array>
+		<dict>
+			<key>CFBundleTypeName</key>
+			<string>Lanework Board</string>
+			<key>CFBundleTypeRole</key>
+			<string>Editor</string>
+			<key>LSItemContentTypes</key>
+			<array>
+				<string>dev.rzen.indie.kanban-board</string>
+			</array>
+			<key>LSTypeIsPackage</key>
+			<true/>
+		</dict>
+	</array>
 </dict>
 </plist>