Release workshop-v0.3.0 and mark support archives pre-release

[gregjkal]

Part of #55.

Problem

The README Downloads links point at workshop-latest, which resolves to promptforge-workshop-v0.2.0 (published 2026-09-02). The workspace is at 0.3.0 and no workshop-v0.3.0 release exists. The 0.2.0 macOS bundle has no gateway sidecar: Contents/MacOS holds only promptforge-workshop, so the README's description of the three-component installer and the sibling gateway launch does not match what anyone can download. latest.json under workshop-latest also still advertises 0.2.0.

Separately, the GitHub Releases "Latest" badge sits on llama-cuda-blackwell-b10082, so the Releases landing page presents a CUDA support archive as the current release.

Done means

• Tag workshop-v0.3.0 and let release-workshop.yml publish it.
• workshop-latest assets (PromptForge-arm64.dmg, PromptForge-x64.dmg, PromptForge-setup.exe, PromptForge.AppImage, PromptForge.deb, latest.json) all come from the 0.3.0 run.
• PromptForge-arm64.dmg mounted and inspected: Contents/MacOS holds both promptforge-workshop and promptforge-gateway, both reporting 0.3.0.
• llama-cuda-blackwell-* and whisper-lib-* releases marked pre-release so the "Latest" badge lands on a Workshop or gateway release.

Signing is tracked in #53 and is not a prerequisite for this release, but the first signed release should be the next one after this.