MCP: Convert AppKit template into a DAB template (#4018)

## Changes
Convert AppKit template into a DAB template and use `bundle init` for
initialization.

## Why
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might be missing.
For example, were there any decisions behind the change that are not
reflected in the code itself? -->

## Tests
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Author: fjakobs

experimental/apps-mcp/lib/prompts/apps.tmpl

@@ -13,7 +13,7 @@ DATABRICKS APPS DEVELOPMENT
 
 ⚠️ ALWAYS start by scaffolding a new Databricks app using command:
 
-invoke_databricks_cli 'experimental apps-mcp tools init-template https://github.com/databricks/cli --template-dir experimental/apps-mcp/templates/appkit --branch mcp/appkit-bundle --config-json '{"project_name":"my-app-name","app_description":"my-app-description","sql_warehouse_id":"{{if .WarehouseID}}{{.WarehouseID}}{{end}}"}''
+invoke_databricks_cli 'experimental apps-mcp tools init-template https://github.com/databricks/cli --template-dir experimental/apps-mcp/templates/appkit --branch main --config-json '{"project_name":"my-app-name","app_description":"my-app-description","sql_warehouse_id":"{{if .WarehouseID}}{{.WarehouseID}}{{end}}"}''
 
 # Validation
 

experimental/apps-mcp/lib/templates/appkit/.env.tmpl

@@ -0,0 +1,24 @@
+{
+    "properties": {
+      "project_name": {
+        "type": "string",
+        "description": "Project Name",
+        "order": 1,
+        "pattern": "^[A-Za-z0-9_-]+$",
+        "pattern_match_failure_message": "Name must consist of letters, numbers, underscores, or hyphens."
+      },
+      "sql_warehouse_id": {
+        "type": "string",
+        "description": "SQL Warehouse ID",
+        "order": 2
+      },
+      "app_description": {
+        "type": "string",
+        "description": "App Description (Optional)",
+        "default": "A Databricks App powered by Databricks AppKit",
+        "order": 3
+      }
+
+    },
+    "success_message": "\nYour new project has been created in the '{{.project_name}}' directory!"
+  }

experimental/apps-mcp/lib/templates/appkit/databricks.yml

@@ -0,0 +1,5 @@
+DATABRICKS_HOST={{workspace_host}}
+DATABRICKS_WAREHOUSE_ID={{.sql_warehouse_id}}
+DATABRICKS_APP_PORT=8000
+DATABRICKS_APP_NAME=minimal
+FLASK_RUN_HOST=0.0.0.0