feat: add platform detail/edit admin UI and service enhancements

- Add platform detail and edit admin pages with templates and JS
- Add ContentPageService methods: list_all_platform_pages, list_all_vendor_defaults
- Deprecate /admin/platform-homepage route (redirects to /admin/platforms)
- Add migration to fix content_page nullable columns
- Refine platform and vendor context middleware
- Add platform context middleware unit tests
- Update platforms.js with improved functionality
- Add section-based homepage plan documentation

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

static/admin/js/platform-detail.js

@@ -0,0 +1,139 @@
+/**
+ * Platform Detail - Alpine.js Component
+ *
+ * Displays platform overview, stats, and quick actions.
+ */
+
+const platformDetailLog = window.LogConfig.createLogger('PLATFORM_DETAIL');
+
+function platformDetail() {
+  return {
+    // Inherit base layout functionality from init-alpine.js
+    ...data(),
+
+    // Page identification
+    currentPage: 'platform-detail',
+
+    // State
+    platform: null,
+    stats: null,
+    recentPages: [],
+    loading: true,
+    error: null,
+    platformCode: null,
+
+    // Lifecycle
+    async init() {
+      platformDetailLog.info('=== PLATFORM DETAIL PAGE INITIALIZING ===');
+
+      // Duplicate initialization guard
+      if (window._platformDetailInitialized) {
+        platformDetailLog.warn('Platform detail page already initialized, skipping...');
+        return;
+      }
+      window._platformDetailInitialized = true;
+
+      try {
+        // Extract platform code from URL
+        const path = window.location.pathname;
+        const match = path.match(/\/admin\/platforms\/([^\/]+)$/);
+
+        if (match) {
+          this.platformCode = match[1];
+          platformDetailLog.info('Viewing platform:', this.platformCode);
+          await Promise.all([
+            this.loadPlatform(),
+            this.loadRecentPages(),
+          ]);
+        } else {
+          platformDetailLog.error('No platform code in URL');
+          this.error = 'Platform code not found in URL';
+          this.loading = false;
+        }
+
+        platformDetailLog.info('=== PLATFORM DETAIL PAGE INITIALIZATION COMPLETE ===');
+      } catch (error) {
+        window.LogConfig.logError(error, 'Platform Detail Init');
+        this.error = 'Failed to initialize page';
+        this.loading = false;
+      }
+    },
+
+    // API Methods
+    async loadPlatform() {
+      try {
+        const response = await apiClient.get(`/admin/platforms/${this.platformCode}`);
+        this.platform = response;
+        platformDetailLog.info(`Loaded platform: ${this.platformCode}`);
+      } catch (err) {
+        platformDetailLog.error('Error loading platform:', err);
+        this.error = err.message || 'Failed to load platform';
+        throw err;
+      } finally {
+        this.loading = false;
+      }
+    },
+
+    async loadRecentPages() {
+      try {
+        // Load recent content pages for this platform
+        const response = await apiClient.get(`/admin/content-pages?platform_code=${this.platformCode}&limit=5`);
+        this.recentPages = response.items || response || [];
+        platformDetailLog.info(`Loaded ${this.recentPages.length} recent pages`);
+      } catch (err) {
+        platformDetailLog.error('Error loading recent pages:', err);
+        // Non-fatal - don't throw
+        this.recentPages = [];
+      }
+    },
+
+    // Helper Methods
+    getPlatformIcon(code) {
+      const icons = {
+        main: 'home',
+        oms: 'clipboard-list',
+        loyalty: 'star',
+        sitebuilder: 'template',
+      };
+      return icons[code] || 'globe-alt';
+    },
+
+    getPageTypeLabel(page) {
+      if (page.is_platform_page) return 'Marketing';
+      if (page.vendor_id) return 'Vendor Override';
+      return 'Vendor Default';
+    },
+
+    getPageTypeBadgeClass(page) {
+      if (page.is_platform_page) {
+        return 'bg-purple-100 text-purple-800 dark:bg-purple-900 dark:text-purple-200';
+      }
+      if (page.vendor_id) {
+        return 'bg-teal-100 text-teal-800 dark:bg-teal-900 dark:text-teal-200';
+      }
+      return 'bg-blue-100 text-blue-800 dark:bg-blue-900 dark:text-blue-200';
+    },
+
+    formatDate(dateString) {
+      if (!dateString) return '—';
+      const date = new Date(dateString);
+      return date.toLocaleDateString('fr-LU', {
+        year: 'numeric',
+        month: 'short',
+        day: 'numeric',
+      });
+    },
+
+    getPlatformUrl() {
+      if (!this.platform) return '#';
+      if (this.platform.domain) {
+        return `https://${this.platform.domain}`;
+      }
+      // Development URL
+      if (this.platform.code === 'main') {
+        return '/';
+      }
+      return `/platforms/${this.platform.code}/`;
+    },
+  };
+}