Add dynamic site name/title configuration

[heysamtexas]

Description

Allow admins to configure the site name/title dynamically through the Django admin interface instead of hardcoding it.

Current State

Site name is handled through context processor but not configurable via admin.

Proposed Implementation

Add field to SiteConfiguration model:

• site_name - CharField for the main site title
• site_tagline - CharField for optional subtitle/tagline

Benefits

• No code deployments needed to change branding
• Consistent site naming across all templates
• Admin-friendly configuration

Acceptance Criteria

• Add site_name field to SiteConfiguration model
• Update context processor to use dynamic value
• Update all templates to use context variable
• Add migration for the new field
• Test admin interface updates

Labels: enhancement, ui/ux
Priority: Medium