Milestone 1: Add Numbers Zapier app, /v1/add, developer setup guide

packages/verae-activate is pushable with zapier-platform 19.1.0: local
Add Numbers (number1+number2=sum) needs no hosted API. zapier-platform
validate is clean (0 warnings). zappier POST /v1/add is a free metered
endpoint for the optional hosted path.

Tests: verae-activate 7/7, zappier 176/176, verae-zapier 5/5, middleware
gate 1 11/11. Morning steps: docs/04-activate/SETUP-ZAPIER-DEVELOPER.md

Learned: perform runs on Zapier cloud so arithmetic needs no public URL;
CLI and zapier-platform-core majors must match; do not mix zapier-sdk.

packages/zappier/openapi.yaml

@@ -58,6 +58,27 @@ paths:
       responses:
         '200':
           description: OK
+  /v1/add:
+    post:
+      operationId: add
+      summary: Add two numbers (activate-now sample)
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              required: [number1, number2]
+              properties:
+                number1:
+                  type: number
+                  description: First addend
+                number2:
+                  type: number
+                  description: Second addend
+      responses:
+        '200':
+          description: OK
   /v1/usage:
     get:
       operationId: usage