chore(deps): upgrade Bun to 1.4.0 and refresh root lockfile

[renovate]

Summary

• Upgrade the repository Bun toolchain declaration from 1.3.13 to 1.4.0.
• Refresh the root bun.lock to lockfile format v2.
• Keep frozen-lockfile installation enabled.

Why

Renovate generated a v2 lockfile, but CI still installed Bun 1.3.13, which cannot parse that format. This caused Linux and Windows dependency installation to fail before tests ran.

Closes #29 after the documentation-site lockfile is also validated and merged.

Verification

• Previous CI failure was confirmed as Unknown lockfile version under Bun 1.3.13.
• Bun 1.4.0 is the current declared toolchain in this PR and supports lockfile v2.
• Fresh hosted CI for commit fe6c6bb4956afe00b76a88c89bcae1dc42069509 is pending.
• No local full suite was claimed; merge remains gated on hosted checks.

Checklist

• I kept the change focused on a single logical unit.
• I updated package metadata and the directly associated root lockfile together.
• I reported the previously failing check and the pending verification honestly.
• I did not add CI, platform-specific files, or application source files to the default mf init template.

[renovate]

Edited/Blocked Notification

Renovate will not automatically rebase this PR, because it does not recognize the last commit author and assumes somebody else may have edited the PR.

You can manually request rebase by checking the rebase/retry box above.

⚠️ Warning: custom changes will be lost.