Local MOD Browser 2.5.1

Public packaging and community release.\n\nHighlights:\n- Complete English README and improved first-run documentation.\n- Public roadmap, CODEOWNERS, PR template, and reviewed contribution workflow.\n- GitHub social-preview artwork and a reproducible source ZIP with SHA-256 checksum.\n\nThe application API contract remains 2.5.0. This patch release improves public packaging and contributor experience without changing the contract.\n\nThe project remains local-first: it does not download, redistribute, install, or execute MOD files.