Upgrade semantic-release tooling

[jleo3]

Summary

• upgrade semantic-release to 25.0.8 and @semantic-release/exec to 7.1.0
• preserve stable and beta release-channel configuration and validate the complete plugin graph
• add regression coverage for stable/beta version propagation, Chrome-compatible manifest versions, ZIP contents, and GitHub release asset metadata
• allow packaging tests to skip the build step explicitly while retaining production packaging behavior

Why

The release toolchain needed its major-version upgrade verified against the repository's Node 24 runtime and existing commit-analyzer, release-notes, GitHub, Git, and exec plugins. The added packaging contract tests make version and artifact behavior explicit before future release changes.

Validation

• npm ci under Node 24.15.0
• 258 unit tests
• ESLint and Prettier checks
• production Webpack build
• 4 Chrome extension E2E tests
• stable-channel semantic-release dry run through release analysis
• beta-channel semantic-release dry run calculating 2.5.4-beta.1 while skipping prepare, tag, publish, and success steps
• disposable full packaging smoke test for 3.1.0-beta.2, including dist/just-not-sorry-chrome.zip
• confirmed no tags, releases, or release ZIP were created by dry-run verification

Closes #196