Convert all schemas to flat format with inline required/secret

All schemas (parameters, output, output_schema, conf_schema) now use the
StackStorm-style flat format expected by Attune:
  { param_name: { type, description, required, secret, ... } }

Instead of the standard JSON Schema format:
  { type: object, properties: { ... }, required: [...] }

Also fix rule template syntax: trigger.payload.* -> event.payload.*

actions/hello.yaml

@@ -19,24 +19,19 @@ parameter_format: json
 # Output format: json (structured data parsing enabled)
 output_format: json
 
-# Action parameters schema (standard JSON Schema format)
+# Action parameters schema (flat format with inline required/secret)
 parameters:
-  type: object
-  properties:
-    name:
-      type: string
-      description: "Optional name to include in greeting"
-      default: "Python"
+  name:
+    type: string
+    description: "Optional name to include in greeting"
+    default: "Python"
 
-# Output schema
+# Output schema (flat format)
 output_schema:
-  type: object
-  properties:
-    message:
-      type: string
-      description: "The greeting message"
-  required:
-    - message
+  message:
+    type: string
+    description: "The greeting message"
+    required: true
 
 # Tags for categorization
 tags: