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/verae-activate/creates/add_numbers.js

@@ -0,0 +1,94 @@
+/**
+ * Add Numbers — Zapier create that needs no backend.
+ *
+ * Inputs: number1, number2 (Zapier number fields).
+ * Output: { number1, number2, sum, mode }.
+ *
+ * If both api_base and api_key are set on the connection, POST /v1/add on the
+ * zappier commercial edge instead of adding locally.
+ *
+ * @module creates/add_numbers
+ */
+
+/**
+ * @param {unknown} value
+ * @param {string} name
+ * @returns {number}
+ */
+function toFiniteNumber(value, name) {
+  const n = typeof value === 'number' ? value : Number(value);
+  if (!Number.isFinite(n)) {
+    throw new Error(`${name} must be a finite number`);
+  }
+  return n;
+}
+
+/**
+ * @param {object} z Zapier z toolkit
+ * @param {object} bundle
+ * @param {object} bundle.inputData
+ * @param {string|number} bundle.inputData.number1
+ * @param {string|number} bundle.inputData.number2
+ * @param {object} bundle.authData
+ * @returns {Promise<{number1: number, number2: number, sum: number, mode: string}>}
+ */
+const perform = async (z, bundle) => {
+  const number1 = toFiniteNumber(bundle.inputData.number1, 'number1');
+  const number2 = toFiniteNumber(bundle.inputData.number2, 'number2');
+  const base = (bundle.authData.api_base || process.env.ZAPPIER_API_BASE || '').replace(/\/$/, '');
+  const key = bundle.authData.api_key || '';
+
+  if (base && key) {
+    const response = await z.request({
+      method: 'POST',
+      url: `${base}/v1/add`,
+      headers: { 'x-api-key': key, 'content-type': 'application/json' },
+      body: { number1, number2 },
+    });
+    const data = response.data || {};
+    return {
+      number1: data.number1 ?? number1,
+      number2: data.number2 ?? number2,
+      sum: data.sum,
+      mode: 'hosted',
+    };
+  }
+
+  return { number1, number2, sum: number1 + number2, mode: 'local' };
+};
+
+module.exports = {
+  key: 'add_numbers',
+  noun: 'Sum',
+  display: {
+    label: 'Add Numbers',
+    description: 'Adds number1 and number2. Works with no API — use this to prove the Zapier connection.',
+  },
+  operation: {
+    cleanInputData: false,
+    inputFields: [
+      {
+        key: 'number1',
+        label: 'Number 1',
+        type: 'number',
+        required: true,
+        helpText: 'First addend.',
+      },
+      {
+        key: 'number2',
+        label: 'Number 2',
+        type: 'number',
+        required: true,
+        helpText: 'Second addend.',
+      },
+    ],
+    perform,
+    sample: { number1: 2, number2: 3, sum: 5, mode: 'local' },
+    outputFields: [
+      { key: 'number1', label: 'Number 1', type: 'number' },
+      { key: 'number2', label: 'Number 2', type: 'number' },
+      { key: 'sum', label: 'Sum', type: 'number' },
+      { key: 'mode', label: 'Mode', type: 'string' },
+    ],
+  },
+};