docs: July 2026 roadmap refresh

Restructure roadmap to reflect the July 1 planning session:

- Add at-a-glance table for quick visual overview of all categories
- Add June 2026 accomplishments section (90+ PRs, 150+ issues)
- Replace June workstream categories with nine July categories
  ordered by team dot-vote priority: BYOA, Infrastructure,
  Observability, Testing, External Partnerships, JIRA, mint,
  Agent Data Access, Exploration
- Move Foundation (April-May) to bottom as historical context
- Ensure all "examples of work" bullets link to tracked issues

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ascerra