Simplify marketplace maintenance, CI, and plugin downloads

[JerryLinLinLin]

Marketplace documentation now separates product overviews, setup guides, release details, and maintainer procedures. Plugin READMEs stay independent of current versions, and shared documentation links also work from extracted plugin packages.

• Generate compatibility manifests from each canonical plugin manifest and check catalog identities, runtime pins, bundled skills, documentation links, and README version policy.
• Use one PR workflow with fast checks for all plugins and Windows validation only when relevant inputs change. Cancel obsolete runs and upload build artifacts only for manual runs.
• Package skills only inside complete plugin ZIPs, with inventories and checksums.
• Move the retained RetDec SDK into a dedicated, hash-pinned asset before retiring the old release that supplied it. Published application binaries remain unchanged.

Public release cleanup removes superseded releases and obsolete standalone skill/plugin downloads, keeps active runtime dependencies, and shortens release notes to user-facing changes and download links.

Validation: marketplace checks and deliberate drift cases passed; CI selection and packaging checks passed. The extracted SDK's 3,866 source files match the original archive, an actual RetDec plugin build linked successfully, and the published SDK checksum was verified after download. Existing runtime archive hashes are preserved.