docs: fix markdownlint violations in the ecosystem integrity plan

- Promote the four workstream headings and Execution Order / Self-Review
  from H1 to H2 so the document has a single top-level title (MD025) and
  heading levels increment by one (MD001).
- Convert hard tabs to spaces in every code block (MD010).

Claude-Session: https://claude.ai/code/session_01MTUKadN91fcmuhxGWYVe2k

Author: Patel230