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/api/migrations/0021_merchant_applications.sql

@@ -0,0 +1,69 @@
+-- Merchant onboarding: a prospective seller (personal 个人 or enterprise 企业)
+-- applies once, a platform admin reviews it, and approval provisions the shop
+-- and its dedicated shop_owner account in one transaction.
+
+CREATE TYPE merchant_entity_type AS ENUM ('personal', 'enterprise');
+CREATE TYPE merchant_application_status AS ENUM ('pending', 'approved', 'rejected');
+
+CREATE TABLE merchant_applications (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id UUID NOT NULL REFERENCES users (id) ON DELETE CASCADE,
+    entity_type merchant_entity_type NOT NULL,
+    -- Personal-kind entity information.
+    real_name TEXT,
+    -- Enterprise-kind entity information.
+    company_name TEXT,
+    business_license_no TEXT,
+    -- Operating categories, one or more rows of the reference category tree.
+    category_ids UUID[] NOT NULL DEFAULT '{}',
+    -- Contact details, shared by both kinds.
+    contact_name TEXT NOT NULL,
+    contact_phone TEXT NOT NULL,
+    contact_email TEXT NOT NULL,
+    contact_address TEXT,
+    -- Qualification materials are URLs only; no file storage in this MVP.
+    identity_document_url TEXT,
+    business_license_url TEXT,
+    extra_materials JSONB NOT NULL DEFAULT '[]'::jsonb,
+    status merchant_application_status NOT NULL DEFAULT 'pending',
+    rejection_reason TEXT,
+    reviewed_by UUID REFERENCES users (id),
+    reviewed_at TIMESTAMPTZ,
+    -- Shop created by approval; null until then.
+    created_shop_id UUID REFERENCES shops (id),
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    -- Each kind carries its own required entity + qualification fields.
+    CONSTRAINT merchant_applications_kind_fields CHECK (
+        (
+            entity_type = 'personal'
+            AND real_name IS NOT NULL AND btrim(real_name) <> ''
+            AND identity_document_url IS NOT NULL AND btrim(identity_document_url) <> ''
+        )
+        OR (
+            entity_type = 'enterprise'
+            AND company_name IS NOT NULL AND btrim(company_name) <> ''
+            AND business_license_url IS NOT NULL AND btrim(business_license_url) <> ''
+        )
+    ),
+    -- A pending row is unreviewed; terminal rows record who and when, and a
+    -- rejection always carries its reason.
+    CONSTRAINT merchant_applications_review_consistent CHECK (
+        (status = 'pending' AND reviewed_by IS NULL AND reviewed_at IS NULL
+            AND rejection_reason IS NULL AND created_shop_id IS NULL)
+        OR (status = 'approved' AND reviewed_by IS NOT NULL AND reviewed_at IS NOT NULL
+            AND rejection_reason IS NULL AND created_shop_id IS NOT NULL)
+        OR (status = 'rejected' AND reviewed_by IS NOT NULL AND reviewed_at IS NOT NULL
+            AND rejection_reason IS NOT NULL AND btrim(rejection_reason) <> ''
+            AND created_shop_id IS NULL)
+    ),
+    CONSTRAINT merchant_applications_categories CHECK (cardinality(category_ids) >= 1)
+);
+
+-- At most one live application per user; rejected rows are free to retry.
+CREATE UNIQUE INDEX merchant_applications_active_idx
+    ON merchant_applications (user_id) WHERE status IN ('pending', 'approved');
+CREATE INDEX merchant_applications_user_idx
+    ON merchant_applications (user_id, created_at DESC);
+CREATE INDEX merchant_applications_status_idx
+    ON merchant_applications (status, created_at DESC);