feat(webui): add SVG icons for forges and adapters on landing page

[nextlevelshit]

Description

The landing page currently shows forge and adapter names as plain text. Add SVG icons for each supported forge (GitHub, GitLab, Bitbucket) and adapter (claude-code, browser, mock) to improve visual clarity and make the dashboard more approachable for first-time users.

Scope

• Forges: GitHub, GitLab, Bitbucket
• Adapters: claude-code, browser, mock
• Location: Landing page dashboard (internal/webui/)

Acceptance Criteria

• SVG icons for each forge type displayed alongside forge names
• SVG icons for each adapter type displayed alongside adapter names
• Icons are consistent in style and size (recommend 20x20px inline SVGs)
• Fallback to text-only display if icons fail to load
• Icons work in both light and dark themes (use currentColor or CSS variables)
• Icons are embedded as inline SVG in templates (no external asset loading)

Implementation Notes

• Inline SVG preferred over external files since webui uses Go html/template with embedded assets
• Use currentColor fill so icons inherit text color across themes
• Consider a shared icons.go or template partial for reuse across pages