feat(i18n): complete post-launch i18n phases 5-8

- Phase 5: Translate homepage-modern.html (~90 new locale keys, all
  hardcoded strings replaced with _() calls for dashboard mock,
  features, pricing tiers, testimonial sections)
- Phase 6: Translate homepage-minimal.html (17 new locale keys for
  fallback content, features, and CTA sections)
- Phase 7: Add multi-language page.title/content support with
  title_translations and content_translations JSON columns, Alembic
  migration cms_002, translated title/content resolution in templates,
  and seed script updates with tt() helper
- Phase 8: Complete lb.json audit — fill 6 missing keys (messages,
  confirmations), also backfill same keys in fr.json and de.json

All 4 locale files now have 340 keys with full parity.

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

app/modules/marketplace/templates/marketplace/platform/find-shop.html

@@ -160,7 +160,7 @@ function storeFinderData() {
                 this.result = await response.json();
             } catch (error) {
                 console.error('Lookup error:', error);
-                this.result = { found: false, error: 'Failed to lookup. Please try again.' };
+                this.result = { found: false, error: '{{ _("cms.platform.find_shop.error_lookup") }}' };
             } finally {
                 this.loading = false;
             }