feat: wave 2 migration (P3, P5, P7 openspec changes)

Implements, verifies, and archives the three remaining Wave 2 changes from
openspec/MIGRATION-PLAN.md.

- add-wallet-settlement (P3): demo recharge, guarded withdrawal freeze and
  one-time admin review, paginated own fund entries, idempotent per-shop
  weekly/monthly settlement statements with commission rate and one-time
  payout confirmation.
- add-merchant-onboarding (P5): personal/enterprise applications with one live
  application per user, guarded review with mandatory rejection reason, and
  transactional shop + owner provisioning returning one-time credentials;
  mall onboarding/status pages and an admin review console.
- add-membership-messaging (P7): platform member levels, append-only growth
  accrual on order completion with guarded one-way leveling, order/shipment/
  refund system messages with unread/read state and soft deletion, plus the
  mall header unread badge.

Backend: migrations 0019-0023, new wallet, settlement, merchant_onboarding,
membership and messaging modules, event hooks in order/fulfillment/aftersale,
and integration suites for each. Shared contract extended and all three
frontends updated; code indexes, domain docs, backend guidelines and the
migration tracker synced.

Verification: cargo test -p vmall-api green twice consecutively; mall, admin
and shop-admin builds pass; browser smoke on every new surface; openspec
validate --all --strict green (33 passed).

The three changes share the @vmall/shared contract, the mall mock adapter and
per-app locale/nav files, so they are committed together to keep every commit
buildable.

apps/mall/locales/shell.ts

@@ -34,6 +34,7 @@ export default {
         v4: "448 service centers nationwide",
         copyright: "VMall Demo Mall — all content is fixed mock data.",
         icp: "Mock ICP 2026-0001",
+        sellerJoin: "Become a Seller",
       },
       backToTop: "Top",
     },
@@ -72,6 +73,7 @@ export default {
         v4: "448家维修网点 全国联保",
         copyright: "VMall 演示商城 —— 所有内容均为固定 mock 数据。",
         icp: "模拟备案号 2026-0001",
+        sellerJoin: "成为商家",
       },
       backToTop: "顶部",
     },