[codex] Prepare 2.0.0-beta.3 prerelease

[hackjutsu]

Summary

Bumps the app metadata from 2.0.0-beta.2 to 2.0.0-beta.3 for another prerelease validation pass after the global content search merge.

Changed files:

• package.json
• package-lock.json
• license.json

Suggested GitHub prerelease notes

For users

• Adds full content search across downloaded snippet file contents, not just descriptions, languages, and file names.
• Shows richer search results with match source labels, highlighted snippets, file context, and updated timestamps.
• Keeps the refreshed Lepton logo and visual assets from the 2.0 prerelease line.
• Includes the 2.0 modernization work: newer Electron/React runtime, safer GitHub OAuth handling, sandboxed renderer/preload boundary, built-in themes, Markdown/AsciiDoc/rendering improvements, and improved syntax highlighting.

For release testing

• Publishes unsigned macOS, Windows, and Linux prerelease artifacts through GitHub Actions.
• Builds macOS artifacts for both Intel (x64) and Apple Silicon (arm64).
• Publishes the Snap prerelease to the edge channel when Snap credentials are available.
• Keeps prerelease builds from notifying stable users through the auto-updater policy.

Known notes

• macOS and Windows builds are intentionally unsigned, so first launch may require the normal OS security override.
• Complete content search depends on downloaded snippet details. Enable snippet.downloadAll to index all snippet file contents during sync.

Validation

• npm test
• npm run lint
• git diff --check
• npm run test:smoke

Additional check

npm version 2.0.0-beta.3 --no-git-tag-version currently cannot complete the repo's preversion hook because npm run check-outdated exits non-zero for known outdated dependencies. The actual release workflow gates on lint, unit tests, and build verification, matching the validation above.