feat: implement section-based homepage management system

Add structured JSON sections to ContentPage for multi-language homepage editing:

Database:
- Add `sections` JSON column to content_pages table
- Migration z8i9j0k1l2m3 adds the column

Schema:
- New models/schema/homepage_sections.py with Pydantic schemas
- TranslatableText for language-keyed translations
- HeroSection, FeaturesSection, PricingSection, CTASection

Templates:
- New section partials in app/templates/platform/sections/
- Updated homepage-default.html to render sections dynamically
- Fallback to placeholder content when sections not configured

Service:
- update_homepage_sections() - validate and save all sections
- update_single_section() - update individual section
- get_default_sections() - empty structure for new homepages

API:
- GET /{page_id}/sections - get sections with platform languages
- PUT /{page_id}/sections - update all sections
- PUT /{page_id}/sections/{section_name} - update single section

Admin UI:
- Section editor appears when editing homepage (slug='home')
- Language tabs from platform.supported_languages
- Accordion sections for Hero, Features, Pricing, CTA
- Button/feature card repeaters with add/remove

Also fixes broken line 181 in z4e5f6a7b8c9 migration.

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

models/database/content_page.py

@@ -29,6 +29,7 @@ Features:
 from datetime import UTC, datetime
 
 from sqlalchemy import (
+    JSON,
     Boolean,
     Column,
     DateTime,
@@ -107,6 +108,16 @@ class ContentPage(Base):
     # Only used for landing pages (slug='landing' or 'home')
     template = Column(String(50), default="default", nullable=False)
 
+    # Homepage sections (structured JSON for section-based editing)
+    # Only used for homepage (slug='home'). Contains hero, features, pricing, cta sections
+    # with multi-language support via TranslatableText pattern
+    sections = Column(
+        JSON,
+        nullable=True,
+        default=None,
+        comment="Structured homepage sections (hero, features, pricing, cta) with i18n",
+    )
+
     # SEO
     meta_description = Column(String(300), nullable=True)
     meta_keywords = Column(String(300), nullable=True)
@@ -199,6 +210,7 @@ class ContentPage(Base):
             "content": self.content,
             "content_format": self.content_format,
             "template": self.template,
+            "sections": self.sections,
             "meta_description": self.meta_description,
             "meta_keywords": self.meta_keywords,
             "is_published": self.is_published,