feat(jobs): add BackgroundColor and Formats to FaviconJob

[GustavoGutierrez]

Context

A DevForge MCP audit (PRP 003, release v2.5.1) confirmed that the generate_favicon handler reads two user-supplied input fields that are silently dropped before reaching dpf because the corresponding FaviconJob protocol struct does not have matching fields.

What's missing in dpf

FaviconJob currently exposes only input and sizes. The following user-supplied fields have no place to go:

• background_color: string — hex color used to paint the icon background (e.g. #ffffff)
• formats: []string — desired output formats (ico, png, svg)

What DevForge will do once this lands

In internal/tools/generate_favicon.go, the handler reads input.BackgroundColor and input.Formats but currently only uses them in a Go-side synth fallback. Once FaviconJob gains these fields, the handler will pass them through to the primary dpf path. The DevForge tool description in cmd/devforge-mcp/main.go will be updated to remove the ''only-in-fallback'' qualifier.

Impact

Today, callers asking for a red background or PNG-only favicon get the default behavior silently. After this lands, the user-supplied values are honored on the primary path.

References

• DevForge commits: 3d1884b (PRP 003 refactor), 5235038 (review fixes)
• DevForge release: v2.5.1
• DevForge memory: prp/003-tools-efficiency-and-reuse/preexisting-bugs