Add Zod validation, fix mass assignment, remove test endpoints and dead code

- Add centralized Zod schemas (server/utils/schemas.js) and validateBody
  utility for all API endpoints
- Fix critical mass assignment in member creation: raw body no longer
  passed to new Member(), only validated fields (email, name, circle,
  contributionTier) are accepted
- Apply Zod validation to login, profile patch, event registration,
  updates, verify-payment, and admin event creation endpoints
- Fix logout cookie flags to match login (httpOnly: true, secure
  conditional on NODE_ENV)
- Delete unauthenticated test/debug endpoints (test-connection,
  test-subscription, test-bot)
- Remove sensitive console.log statements from Helcim and member
  endpoints
- Remove unused bcryptjs dependency
- Add 10MB file size limit on image uploads
- Use runtime config for JWT secret across all endpoints
- Add 38 validation tests (117 total, all passing)

server/utils/validateBody.js

@@ -0,0 +1,12 @@
+export async function validateBody(event, schema) {
+  const body = await readBody(event)
+  const result = schema.safeParse(body)
+  if (!result.success) {
+    throw createError({
+      statusCode: 400,
+      statusMessage: 'Validation failed',
+      data: result.error.flatten().fieldErrors
+    })
+  }
+  return result.data
+}