docs: refresh README for v0.2.0

[teedole]

Summary

• Replace the README hero image with the current v0.2.0 Analytics UI, rendered from synthetic fixtures.
• Make npx @dosu/decant@latest serve the primary zero-install quick start and distinguish it from a persistent global npm install.
• Remove the redundant Homebrew formula version stanza from the release template and add a regression test.

Why

The README screenshot and onboarding path should match the v0.2.0 experience. The release template also emitted an explicit version that Homebrew 6 now rejects in the tap-wide audit because the version is inferable from the release URLs.

Validation

• just check passes: 783 tests, TypeScript, Biome, and distribution staging smoke.
• New behavior has a focused distribution test. No existing test was weakened or deleted.
• Playwright captured the current UI at 1440 x 1024 CSS pixels (2x device scale) from a scratch archive containing only synthetic fixtures.
• The rendered v0.2.0 Homebrew template exactly matches the corrected live tap formula.

Archive schema

• This change does not touch the archive schema.
• This change bumps the schema. It ships the migration, and the summary above says what happens to archives created before it.

[gemini-code-assist]

Code Review

This pull request updates the documentation in README.md to recommend running Decant using npx @dosu/decant@latest and moves the source-run instructions to a separate note. It also removes the redundant version stanza from the Homebrew formula template (decant.rb.template) to comply with Homebrew's tap-wide audit requirements, and adds a corresponding unit test in distribution.test.ts to prevent regressions. There are no review comments, and I have no additional feedback to provide.