fix(server): treat contributionAmount as cadence-unit (drop ×12)

ContributionAmountField now emits cadence-unit values (180 for $180/yr,
15 for $15/mo). Server endpoints were still multiplying annual by 12,
which would have charged $2160/yr instead of $180/yr after the form
ports in Tasks 2–3.

- helcim/subscription.post.js: recurringAmount = contributionAmount
  (no more × 12 for annual)
- members/update-contribution.post.js: same drop in both Case 1
  (free→paid) and Case 3 (paid→paid)
- slack.ts notifyNewMember: new positional `cadence` param so the
  Slack notification suffix renders /yr or /mo instead of hardcoded
  /month; all three call sites updated to pass member.billingCadence
- tests updated to match the new contract:
  - helcim-subscription.test.js: annual tests now send the cadence-
    unit amount (180, 600) and expect the same recurringAmount
  - update-contribution.test.js: annual Case 1 and Case 3 tests
    updated likewise

server/api/helcim/subscription.post.js

@@ -47,6 +47,7 @@ export default defineEventHandler(async (event) => {
             member.email,
             member.circle,
             member.contributionAmount,
+            member.billingCadence,
             'manual_invitation_required'
           )
         }
@@ -79,9 +80,7 @@ export default defineEventHandler(async (event) => {
 
     const cadence = body.cadence
     const paymentPlanId = getHelcimPlanId(cadence)
-    const recurringAmount = cadence === 'annual'
-      ? body.contributionAmount * 12
-      : body.contributionAmount
+    const recurringAmount = body.contributionAmount
 
     if (!paymentPlanId) {
       throw createError({
@@ -159,6 +158,7 @@ export default defineEventHandler(async (event) => {
           member.email,
           member.circle,
           member.contributionAmount,
+          member.billingCadence,
           'manual_invitation_required'
         )
       }

server/api/members/create.post.js

@@ -43,6 +43,7 @@ export default defineEventHandler(async (event) => {
           member.email,
           member.circle,
           member.contributionAmount,
+          member.billingCadence,
           'manual_invitation_required'
         )
       }

server/api/members/update-contribution.post.js

@@ -88,7 +88,7 @@ export default defineEventHandler(async (event) => {
             dateActivated: new Date().toISOString().split("T")[0],
             paymentPlanId: parseInt(paymentPlanId),
             customerCode,
-            recurringAmount: cadence === 'annual' ? newAmount * 12 : newAmount,
+            recurringAmount: newAmount,
             paymentMethod: "card",
           },
           idempotencyKey,
@@ -217,7 +217,7 @@ export default defineEventHandler(async (event) => {
       try {
         const subscriptionData = await updateHelcimSubscription(
           member.helcimSubscriptionId,
-          { recurringAmount: memberCadence === 'annual' ? newAmount * 12 : newAmount }
+          { recurringAmount: newAmount }
         );
 
         await Member.findByIdAndUpdate(

server/utils/slack.ts

@@ -90,6 +90,7 @@ export class SlackService {
     memberEmail: string,
     circle: string,
     contributionAmount: number,
+    cadence: string = 'monthly',
     invitationStatus: string = "manual_invitation_required",
   ): Promise<void> {
     try {
@@ -148,7 +149,7 @@ export class SlackService {
               },
               {
                 type: "mrkdwn",
-                text: `*Contribution:*\n$${contributionAmount}/month`,
+                text: `*Contribution:*\n$${contributionAmount}/${cadence === 'annual' ? 'yr' : 'mo'}`,
               },
             ],
           },