Prepare Viewer alpha for the Changesets release

[kvz]

Why

Complete the existing Changesets release train in #502 with the first public Viewer alpha. Package publication is separate from enabling Storage: the Storage APIs, Built-ins and device login still require the matching API2/Console deployment, owned by Kevin and the deployer agent. Existing origin-pinned HTTP/S3 Templates remain independently usable.

Changes

• Make @transloadit/viewer publishable and add a patch changeset (expected first version: 0.0.1), with explicit alpha/API-instability documentation.
• Publish Viewer with an explicit alpha tag before Changesets publishes the stable packages. Changesets itself overrides publishConfig.tag with latest; its normal version PR and tag/release discovery remain authoritative.
• Fail closed on registry lookup errors and skip already-published versions on retry.
• Remove Viewer's recursive TypeScript clean, which could delete Utils artifacts during concurrent packaging.
• Include Utils and Viewer in the release packaging dry run; lock the fixture's external Utils dependency.
• Record the complete release gates and the subsequent Content/Console/CLI dogfood sequence.

No versions or generated changelogs were edited by hand. Review the generated #502 Viewer dependency floor (@transloadit/utils >=4.9.0) and verify npm tags/GitHub prerelease status after publication.

Verification

• Metadata and both council findings reproduced with failing tests before fixes; all 37 focused tests now pass.
• corepack yarn verify:full, corepack yarn check, corepack yarn knip and corepack yarn release:pack:dry-run pass.
• Packed Next fixture: Chromium and WebKit; 58 cases with cacheComponents, 58 without, secretless public builds, plus 10 development checks.
• Independent council follow-up: no further findings. Claude's legs were unavailable due to its monthly spend limit; they are not counted as successful reviews.
• Explicit TypeScript check of the new publishing entry point passes.

Preparation for #502.