Typescript migration of __mocks__/gatsby.js

Editor assessment

The header is serviceable — `chore(client)` scopes correctly and the migrated file is named — but 'Typescript' should be lowercase and the type is arguably refactor, since a JS-to-TS migration usually preserves behavior. The real problem is the body: it merely repeats the exact header line twice as squash fragments, adding zero information while cluttering the log with duplication and stray carriage returns. Either summarize what the migration entailed (types added, mocks adjusted) or omit the body entirely. As written, full-format git log shows the same sentence three times.