docs(openspec): propose 8 tigshop migration changes (P0-P7) + migration plan

openspec/changes/add-merchant-onboarding/specs/frontend-admin/spec.md

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+## ADDED Requirements
+
+### Requirement: Merchant application review console
+Platform admins SHALL review merchant onboarding applications in a dedicated console entry beside existing platform operations: a status-filtered paginated list and a detail view showing entity kind, entity information, operating categories, contact details, and qualification URL fields. Approving SHALL provision the shop and `shop_owner` account and display the one-time initial credentials exactly once, with copy stating the password cannot be retrieved again. Rejecting SHALL require a reason. Reviewed applications SHALL leave the pending queue immediately.
+
+#### Scenario: review an enterprise application
+- **WHEN** a platform admin opens a pending enterprise application
+- **THEN** the company entity data, operating categories, contact details, and qualification URLs are visible for review
+
+#### Scenario: approve shows one-time credentials
+- **WHEN** a platform admin approves an application
+- **THEN** the created shop owner's initial credentials are shown once and the application moves to the approved list
+
+#### Scenario: reject requires a reason
+- **WHEN** a platform admin attempts to reject without entering a reason
+- **THEN** the action is blocked until a non-empty reason is provided
+
+#### Scenario: entry beside platform operations
+- **WHEN** an authenticated platform admin opens the admin console
+- **THEN** merchant application review is reachable from the console navigation