feat: production routing support for subdomain and custom domain modes

Double-mount store routes at /store/* and /store/{store_code}/* so the
same handlers work in dev path-based, prod path-based, prod subdomain,
and prod custom-domain modes.  Wire StorePlatform.custom_subdomain into
StoreContextMiddleware for per-platform subdomain overrides.  Add admin
custom-domain management UI, fix stale /shop/ reset link, add
/merchants/ to reserved paths, and server-render window.STORE_CODE for
JS that previously parsed the URL.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/tenancy/static/admin/js/store-detail.js

@@ -20,6 +20,13 @@ function adminStoreDetail() {
         showDeleteStoreModal: false,
         showDeleteStoreFinalModal: false,
 
+        // Domain management state
+        domains: [],
+        domainsLoading: false,
+        showAddDomainForm: false,
+        domainSaving: false,
+        newDomain: { domain: '', platform_id: '' },
+
         // Initialize
         async init() {
             // Load i18n translations
@@ -42,9 +49,12 @@ function adminStoreDetail() {
                 this.storeCode = match[1];
                 detailLog.info('Viewing store:', this.storeCode);
                 await this.loadStore();
-                // Load subscription after store is loaded
+                // Load subscription and domains after store is loaded
                 if (this.store?.id) {
-                    await this.loadSubscriptions();
+                    await Promise.all([
+                        this.loadSubscriptions(),
+                        this.loadDomains(),
+                    ]);
                 }
             } else {
                 detailLog.error('No store code in URL');
@@ -180,6 +190,90 @@ function adminStoreDetail() {
             }
         },
 
+        // ====================================================================
+        // DOMAIN MANAGEMENT
+        // ====================================================================
+
+        async loadDomains() {
+            if (!this.store?.id) return;
+            this.domainsLoading = true;
+            try {
+                const url = `/admin/stores/${this.store.id}/domains`;
+                const response = await apiClient.get(url);
+                this.domains = response.domains || [];
+                detailLog.info('Domains loaded:', this.domains.length);
+            } catch (error) {
+                if (error.status === 404) {
+                    this.domains = [];
+                } else {
+                    detailLog.warn('Failed to load domains:', error.message);
+                }
+            } finally {
+                this.domainsLoading = false;
+            }
+        },
+
+        async addDomain() {
+            if (!this.newDomain.domain || this.domainSaving) return;
+            this.domainSaving = true;
+            try {
+                const payload = { domain: this.newDomain.domain };
+                if (this.newDomain.platform_id) {
+                    payload.platform_id = parseInt(this.newDomain.platform_id);
+                }
+                await apiClient.post(`/admin/stores/${this.store.id}/domains`, payload);
+                Utils.showToast('Domain added successfully', 'success');
+                this.showAddDomainForm = false;
+                this.newDomain = { domain: '', platform_id: '' };
+                await this.loadDomains();
+            } catch (error) {
+                Utils.showToast(error.message || 'Failed to add domain', 'error');
+            } finally {
+                this.domainSaving = false;
+            }
+        },
+
+        async verifyDomain(domainId) {
+            try {
+                const response = await apiClient.post(`/admin/stores/domains/${domainId}/verify`);
+                Utils.showToast(response.message || 'Domain verified!', 'success');
+                await this.loadDomains();
+            } catch (error) {
+                Utils.showToast(error.message || 'Verification failed — check DNS records', 'error');
+            }
+        },
+
+        async toggleDomainActive(domainId, activate) {
+            try {
+                await apiClient.put(`/admin/stores/domains/${domainId}`, { is_active: activate });
+                Utils.showToast(activate ? 'Domain activated' : 'Domain deactivated', 'success');
+                await this.loadDomains();
+            } catch (error) {
+                Utils.showToast(error.message || 'Failed to update domain', 'error');
+            }
+        },
+
+        async setDomainPrimary(domainId) {
+            try {
+                await apiClient.put(`/admin/stores/domains/${domainId}`, { is_primary: true });
+                Utils.showToast('Domain set as primary', 'success');
+                await this.loadDomains();
+            } catch (error) {
+                Utils.showToast(error.message || 'Failed to set primary domain', 'error');
+            }
+        },
+
+        async deleteDomain(domainId, domainName) {
+            if (!confirm(`Delete domain "${domainName}"? This cannot be undone.`)) return;
+            try {
+                await apiClient.delete(`/admin/stores/domains/${domainId}`);
+                Utils.showToast('Domain deleted', 'success');
+                await this.loadDomains();
+            } catch (error) {
+                Utils.showToast(error.message || 'Failed to delete domain', 'error');
+            }
+        },
+
         // Refresh store data
         async refresh() {
             detailLog.info('=== STORE REFRESH TRIGGERED ===');