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/api/v1/admin/content_pages.py

@@ -32,6 +32,7 @@ class ContentPageCreate(BaseModel):
     title: str = Field(..., max_length=200, description="Page title")
     content: str = Field(..., description="HTML or Markdown content")
     content_format: str = Field(default="html", description="Content format: html or markdown")
+    template: str = Field(default="default", max_length=50, description="Template name (default, minimal, modern)")
     meta_description: Optional[str] = Field(None, max_length=300, description="SEO meta description")
     meta_keywords: Optional[str] = Field(None, max_length=300, description="SEO keywords")
     is_published: bool = Field(default=False, description="Publish immediately")
@@ -46,6 +47,7 @@ class ContentPageUpdate(BaseModel):
     title: Optional[str] = Field(None, max_length=200)
     content: Optional[str] = None
     content_format: Optional[str] = None
+    template: Optional[str] = Field(None, max_length=50)
     meta_description: Optional[str] = Field(None, max_length=300)
     meta_keywords: Optional[str] = Field(None, max_length=300)
     is_published: Optional[bool] = None
@@ -120,6 +122,7 @@ def create_platform_page(
         content=page_data.content,
         vendor_id=None,  # Platform default
         content_format=page_data.content_format,
+        template=page_data.template,
         meta_description=page_data.meta_description,
         meta_keywords=page_data.meta_keywords,
         is_published=page_data.is_published,
@@ -202,6 +205,7 @@ def update_page(
         title=page_data.title,
         content=page_data.content,
         content_format=page_data.content_format,
+        template=page_data.template,
         meta_description=page_data.meta_description,
         meta_keywords=page_data.meta_keywords,
         is_published=page_data.is_published,