[techflag]

Prepare Desktop 3.0.0-alpha.3 with the expert agents-home fix merged in #68. The release keeps DSH 0.2.1-rc.2 and the existing platform/runtime boundaries; no application behavior changes are introduced here.

• Increment the Desktop package version and add release notes with the precise fix, verification scope, downloads and existing Alpha/platform limitations.
• Local validation: Desktop and Web DSH alignment checks pass; bilingual-docs and CI-scope tests pass (10/10). The underlying main commit passed Web, enterprise, Windows and both macOS CI jobs; expert integration tests pass (29/29), plus the isolated DSH_HOME-only cold-restart regression.
• After this PR passes checks and merges, tag its main commit, rebuild through the tag release workflow, verify attachments and checksums, then promote the completed GitHub release to Latest. README download links will change only once the new assets are available.