feat: add platform homepage and content management system with improved UI

Implemented a comprehensive CMS for managing platform homepage and content pages:

- Platform homepage manager with template selection (default, minimal, modern)
- Content pages CRUD with platform defaults and vendor overrides
- Sidebar navigation for Content Management section
- Dedicated API endpoints for creating, updating, deleting pages
- Template support for customizable homepage layouts
- Header/footer navigation integration for content pages
- Comprehensive documentation for platform homepage setup
- Migration script for creating initial platform pages

UI improvements:
- Fixed action buttons styling in content pages table to match design system
- Added proper hover states, rounded corners, and better contrast
- Increased button size and padding for better usability

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/services/content_page_service.py

@@ -176,6 +176,7 @@ class ContentPageService:
         content: str,
         vendor_id: Optional[int] = None,
         content_format: str = "html",
+        template: str = "default",
         meta_description: Optional[str] = None,
         meta_keywords: Optional[str] = None,
         is_published: bool = False,
@@ -194,6 +195,7 @@ class ContentPageService:
             content: HTML or Markdown content
             vendor_id: Vendor ID (None for platform default)
             content_format: "html" or "markdown"
+            template: Template name for homepage/landing pages (default, minimal, modern, etc.)
             meta_description: SEO description
             meta_keywords: SEO keywords
             is_published: Publish immediately
@@ -211,6 +213,7 @@ class ContentPageService:
             title=title,
             content=content,
             content_format=content_format,
+            template=template,
             meta_description=meta_description,
             meta_keywords=meta_keywords,
             is_published=is_published,
@@ -236,6 +239,7 @@ class ContentPageService:
         title: Optional[str] = None,
         content: Optional[str] = None,
         content_format: Optional[str] = None,
+        template: Optional[str] = None,
         meta_description: Optional[str] = None,
         meta_keywords: Optional[str] = None,
         is_published: Optional[bool] = None,
@@ -253,6 +257,7 @@ class ContentPageService:
             title: New title
             content: New content
             content_format: New format
+            template: New template name
             meta_description: New SEO description
             meta_keywords: New SEO keywords
             is_published: New publish status
@@ -277,6 +282,8 @@ class ContentPageService:
             page.content = content
         if content_format is not None:
             page.content_format = content_format
+        if template is not None:
+            page.template = template
         if meta_description is not None:
             page.meta_description = meta_description
         if meta_keywords is not None: