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

app/api/chat/route.ts

@@ -609,14 +609,22 @@ Operations:
 
 For update/add, new_xml must be a complete mxCell element including mxGeometry.
 
-⚠️ JSON ESCAPING: Every " inside new_xml MUST be escaped as \\". Example: id=\\"5\\" value=\\"Label\\"`,
+⚠️ JSON ESCAPING: Every " inside new_xml MUST be escaped as \\". Example: id=\\"5\\" value=\\"Label\\"
+
+Example - Add a rectangle:
+{"operations": [{"operation": "add", "cell_id": "rect-1", "new_xml": "<mxCell id=\\"rect-1\\" value=\\"Hello\\" style=\\"rounded=0;\\" vertex=\\"1\\" parent=\\"1\\"><mxGeometry x=\\"100\\" y=\\"100\\" width=\\"120\\" height=\\"60\\" as=\\"geometry\\"/></mxCell>"}]}
+
+Example - Delete a cell:
+{"operations": [{"operation": "delete", "cell_id": "rect-1"}]}`,
                 inputSchema: z.object({
                     operations: z
                         .array(
                             z.object({
-                                type: z
+                                operation: z
                                     .enum(["update", "add", "delete"])
-                                    .describe("Operation type"),
+                                    .describe(
+                                        "Operation to perform: add, update, or delete",
+                                    ),
                                 cell_id: z
                                     .string()
                                     .describe(