refactor: migrate templates and static files to self-contained modules

Templates Migration:
- Migrate admin templates to modules (tenancy, billing, monitoring, marketplace, etc.)
- Migrate vendor templates to modules (tenancy, billing, orders, messaging, etc.)
- Migrate storefront templates to modules (catalog, customers, orders, cart, checkout, cms)
- Migrate public templates to modules (billing, marketplace, cms)
- Keep shared templates in app/templates/ (base.html, errors/, partials/, macros/)
- Migrate letzshop partials to marketplace module

Static Files Migration:
- Migrate admin JS to modules: tenancy (23 files), core (5 files), monitoring (1 file)
- Migrate vendor JS to modules: tenancy (4 files), core (2 files)
- Migrate shared JS: vendor-selector.js to core, media-picker.js to cms
- Migrate storefront JS: storefront-layout.js to core
- Keep framework JS in static/ (api-client, utils, money, icons, log-config, lib/)
- Update all template references to use module_static paths

Naming Consistency:
- Rename static/platform/ to static/public/
- Rename app/templates/platform/ to app/templates/public/
- Update all extends and static references

Documentation:
- Update module-system.md with shared templates documentation
- Update frontend-structure.md with new module JS organization

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

app/modules/tenancy/static/admin/js/platforms.js

@@ -0,0 +1,80 @@
+/**
+ * Platforms Manager - Alpine.js Component
+ *
+ * Handles platform listing and management for multi-platform CMS.
+ */
+
+const platformsLog = window.LogConfig.createLogger('PLATFORMS');
+
+function platformsManager() {
+  return {
+    // Inherit base layout functionality from init-alpine.js
+    ...data(),
+
+    // Page identification
+    currentPage: "platforms",
+
+    // State
+    platforms: [],
+    loading: true,
+    error: null,
+
+    // Lifecycle
+    async init() {
+      platformsLog.info('=== PLATFORMS PAGE INITIALIZING ===');
+
+      // Duplicate initialization guard
+      if (window._adminPlatformsInitialized) {
+        platformsLog.warn('Platforms page already initialized, skipping...');
+        return;
+      }
+      window._adminPlatformsInitialized = true;
+
+      try {
+        await this.loadPlatforms();
+        platformsLog.info('=== PLATFORMS PAGE INITIALIZATION COMPLETE ===');
+      } catch (error) {
+        window.LogConfig.logError(error, 'Platforms Init');
+        this.error = 'Failed to initialize page';
+      }
+    },
+
+    // API Methods
+    async loadPlatforms() {
+      this.loading = true;
+      this.error = null;
+
+      try {
+        const response = await apiClient.get("/admin/platforms");
+        this.platforms = response.platforms || [];
+        platformsLog.info(`Loaded ${this.platforms.length} platforms`);
+      } catch (err) {
+        platformsLog.error("Error loading platforms:", err);
+        this.error = err.message || "Failed to load platforms";
+      } finally {
+        this.loading = false;
+      }
+    },
+
+    // Helper Methods
+    getPlatformIcon(code) {
+      const icons = {
+        oms: "clipboard-list",
+        loyalty: "star",
+        sitebuilder: "template",
+        default: "globe-alt",
+      };
+      return icons[code] || icons.default;
+    },
+
+    formatDate(dateString) {
+      if (!dateString) return "—";
+      const date = new Date(dateString);
+      return date.toLocaleDateString("fr-LU", {
+        year: "numeric",
+        month: "short",
+        day: "numeric",
+      });
+    },
+  };
+}