PR 6: Database migration validation - fresh/upgrade test complete

✅ Database Setup:
- Created PostgreSQL kartselldb with kartsell user
- SSH port forward established (localhost:5432 → 178.104.200.7:5432)

✅ DbMigrator Fixes:
- Fixed migration path discovery (AppContext.BaseDirectory fallback)
- Added empty variable dictionary to suppress DbUp preprocessing
- Fixed PostgreSQL dollar quoting conflict ($policy$ → $$)

✅ Migration Results:
- All 21 migrations executed successfully
- Schema versions journal created and tracked
- 21 scripts processed in order, no rollback needed

Status: FRESH DATABASE DEPLOYMENT SUCCESSFUL
- kartselldb fully initialized with v16 schema
- Ready for application startup

Next: Deploy application and run integration tests

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

frontend/src/shared/ui/adapter/contracts.js

@@ -0,0 +1,22 @@
+export const requiredUiAdapterCapabilities = Object.freeze([
+    'button', 'text-field', 'text-area', 'select', 'multi-select', 'checkbox', 'date-field',
+    'number-field', 'dialog', 'status-tag', 'inline-message', 'paginator', 'tabs', 'data-grid'
+]);
+export function assertUiAdapterContract(adapter) {
+    if (adapter.descriptor.contractVersion !== '4.0') {
+        throw new Error(`Unsupported UI adapter contract: ${adapter.descriptor.contractVersion}`);
+    }
+    const missing = requiredUiAdapterCapabilities.filter(x => !adapter.descriptor.capabilities.has(x));
+    if (missing.length > 0) {
+        throw new Error(`UI adapter ${adapter.descriptor.id} is missing capabilities: ${missing.join(', ')}`);
+    }
+    const componentNames = [
+        'Button', 'TextField', 'TextArea', 'Select', 'MultiSelect', 'Checkbox', 'DateField',
+        'NumberField', 'Dialog', 'StatusTag', 'InlineMessage', 'Paginator', 'Tabs', 'DataGrid'
+    ];
+    for (const name of componentNames) {
+        if (!adapter.components[name])
+            throw new Error(`UI adapter ${adapter.descriptor.id} has no component for ${name}`);
+    }
+}
+export const uiAdapterKey = Symbol('KArtSellUiAdapterV4');