fix: rename edit_diagram type field to operation for better model compatibility (#402)

Fixes #374 - Models were confused by the `type` field name and sent
`operation` instead. This change:

- Renames DiagramOperation.type to DiagramOperation.operation across
  all files (MCP server, web app, hooks, components, system prompts)
- Adds JSON examples in tool descriptions to show correct format
- Updates all test data to use the new field name

Affected files:
- lib/utils.ts
- app/api/chat/route.ts
- hooks/use-diagram-tool-handlers.ts
- components/chat-message-display.tsx
- lib/system-prompts.ts
- packages/mcp-server/src/diagram-operations.ts
- packages/mcp-server/src/index.ts
- scripts/test-diagram-operations.mjs

MCP server version bumped to 0.1.6

lib/utils.ts

@@ -455,7 +455,7 @@ export function replaceNodes(currentXML: string, nodes: string): string {
 // ============================================================================
 
 export interface DiagramOperation {
-    type: "update" | "add" | "delete"
+    operation: "update" | "add" | "delete"
     cell_id: string
     new_xml?: string
 }
@@ -528,7 +528,7 @@ export function applyDiagramOperations(
 
     // Process each operation
     for (const op of operations) {
-        if (op.type === "update") {
+        if (op.operation === "update") {
             const existingCell = cellMap.get(op.cell_id)
             if (!existingCell) {
                 errors.push({
@@ -580,7 +580,7 @@ export function applyDiagramOperations(
 
             // Update the map with the new element
             cellMap.set(op.cell_id, importedNode)
-        } else if (op.type === "add") {
+        } else if (op.operation === "add") {
             // Check if ID already exists
             if (cellMap.has(op.cell_id)) {
                 errors.push({
@@ -632,7 +632,7 @@ export function applyDiagramOperations(
 
             // Add to map
             cellMap.set(op.cell_id, importedNode)
-        } else if (op.type === "delete") {
+        } else if (op.operation === "delete") {
             const existingCell = cellMap.get(op.cell_id)
             if (!existingCell) {
                 errors.push({