[T-42C5A6] Update implementor default prompt

[weekly-daniel]

Summary

Replace the minimal implementor default prompt with a comprehensive prompt covering subagent usage, autonomy, core principles, test verification, and definition of done.

Key Changes

• server/src/config.js (replace the implementation string in DEFAULT_PROMPTS with the expanded prompt)

Review

• Verdict: PASS
• Summary: Changed file: server/src/config.js (plus cosmetic peer flag shuffles in three package-lock.json files). The implementation default prompt in DEFAULT_PROMPTS was expanded from 5 bullet points to a well-structured multi-section prompt covering subagent usage, autonomy, core principles, TDD/test verification, and definition of done. All original guidance (install missing deps, commit after logical units, final commit) is preserved. The new text is a string literal change only — no logic, control flow, or API surface is affected. The prompt aligns with the project's own CLAUDE.md principles, which is a nice consistency win. The package-lock.json diffs are harmless peer-dependency metadata reordering with no functional impact.

Risks

• Users who have not customized their prompts will get the new default on next settings load. Users who have already saved custom prompts are unaffected because normalizeSettingsShape merges saved prompts over defaults.
• Existing server tests should cover this; no new tests needed since the change is a string literal update. RISKS: - Users who have not customized their prompts will get the new default on next settings load. Users who have already saved custom prompts are unaffected because normalizeSettingsShape merges saved prompts over defaults.