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>

app/services/content_page_service.py

@@ -872,6 +872,130 @@ class ContentPageService:
         if not success:
             raise ContentPageNotFoundException(identifier=page_id)
 
+    # =========================================================================
+    # Homepage Sections Management
+    # =========================================================================
+
+    @staticmethod
+    def update_homepage_sections(
+        db: Session,
+        page_id: int,
+        sections: dict,
+        updated_by: int | None = None,
+    ) -> ContentPage:
+        """
+        Update homepage sections with validation.
+
+        Args:
+            db: Database session
+            page_id: Content page ID
+            sections: Homepage sections dict (validated against HomepageSections schema)
+            updated_by: User ID making the update
+
+        Returns:
+            Updated ContentPage
+
+        Raises:
+            ContentPageNotFoundException: If page not found
+            ValidationError: If sections schema invalid
+        """
+        from models.schema.homepage_sections import HomepageSections
+
+        page = ContentPageService.get_page_by_id_or_raise(db, page_id)
+
+        # Validate sections against schema
+        validated = HomepageSections(**sections)
+
+        # Update page
+        page.sections = validated.model_dump()
+        page.updated_by = updated_by
+
+        db.flush()
+        db.refresh(page)
+
+        logger.info(f"[CMS] Updated homepage sections for page_id={page_id}")
+        return page
+
+    @staticmethod
+    def update_single_section(
+        db: Session,
+        page_id: int,
+        section_name: str,
+        section_data: dict,
+        updated_by: int | None = None,
+    ) -> ContentPage:
+        """
+        Update a single section within homepage sections.
+
+        Args:
+            db: Database session
+            page_id: Content page ID
+            section_name: Section to update (hero, features, pricing, cta)
+            section_data: Section configuration dict
+            updated_by: User ID making the update
+
+        Returns:
+            Updated ContentPage
+
+        Raises:
+            ContentPageNotFoundException: If page not found
+            ValueError: If section name is invalid
+        """
+        from models.schema.homepage_sections import (
+            HeroSection,
+            FeaturesSection,
+            PricingSection,
+            CTASection,
+        )
+
+        SECTION_SCHEMAS = {
+            "hero": HeroSection,
+            "features": FeaturesSection,
+            "pricing": PricingSection,
+            "cta": CTASection,
+        }
+
+        if section_name not in SECTION_SCHEMAS:
+            raise ValueError(f"Invalid section name: {section_name}. Must be one of: {list(SECTION_SCHEMAS.keys())}")
+
+        page = ContentPageService.get_page_by_id_or_raise(db, page_id)
+
+        # Validate section data against its schema
+        schema = SECTION_SCHEMAS[section_name]
+        validated_section = schema(**section_data)
+
+        # Initialize sections if needed
+        current_sections = page.sections or {}
+        current_sections[section_name] = validated_section.model_dump()
+
+        page.sections = current_sections
+        page.updated_by = updated_by
+
+        db.flush()
+        db.refresh(page)
+
+        logger.info(f"[CMS] Updated section '{section_name}' for page_id={page_id}")
+        return page
+
+    @staticmethod
+    def get_default_sections(languages: list[str] | None = None) -> dict:
+        """
+        Get empty sections structure for new homepage.
+
+        Args:
+            languages: List of language codes from platform.supported_languages.
+                       Defaults to ['fr', 'de', 'en'] if not provided.
+
+        Returns:
+            Empty sections dict with language placeholders
+        """
+        from models.schema.homepage_sections import HomepageSections
+
+        if languages is None:
+            languages = ["fr", "de", "en"]
+
+        return HomepageSections.get_empty_structure(languages).model_dump()
+
 
 # Singleton instance
 content_page_service = ContentPageService()