feat(idea): create group auto-generates personas; channel removed; product->product/idea

Per product-idea focus:
- GroupBuilder: 'สินค้า/บริการ/ไอเดีย' label; removed the channel select (channel is now
  chosen at chat time as a scenario, not at persona create). Create now auto-runs analyze
  so personas are generated immediately (no separate Analyze button).
- GroupEdit: analyze button becomes 'สร้างบุคคลต้นแบบเพิ่มเติม' which APPENDS more personas
  (backend analyze?append=true reuses sales kit + keeps existing instead of replacing).
- i18n product label updated.
- User-journey test asserts append adds personas (15->30) and existing kept.
All 9 backend suites pass. Rebuilt dist.

frontend/src/api/index.js

@@ -43,7 +43,7 @@ export const api = {
   createGroup: (formData) => request('POST', '/api/groups', formData, true),
   listGroups: () => request('GET', '/api/groups'),
   getGroup: (id) => request('GET', `/api/groups/${id}`),
-  analyzeGroup: (id) => request('POST', `/api/groups/${id}/analyze`),
+  analyzeGroup: (id, opts = {}) => request('POST', `/api/groups/${id}/analyze${opts.append ? '?append=true' : ''}`),
   listPersonas: (gid) => request('GET', `/api/groups/${gid}/personas`),
   getPersona: (gid, pid) => request('GET', `/api/groups/${gid}/personas/${pid}`),
   updatePersona: (gid, pid, b) => request('PUT', `/api/groups/${gid}/personas/${pid}`, b),