chore: complete v1.0 milestone

Archive v1.0 MVP: 7 phases, 13 plans, 27/27 requirements.

- Archive roadmap to milestones/v1.0-ROADMAP.md
- Archive requirements to milestones/v1.0-REQUIREMENTS.md
- Move milestone audit into milestones/
- Create MILESTONES.md with v1.0 entry
- Evolve PROJECT.md: move shipped requirements to Validated,
  update Context with stack/LOC, log Key Decisions with outcomes
- Collapse ROADMAP.md to one-line milestone summary
- Update STATE.md to shipped status
- Back-fill stale requirements-completed frontmatter on
  02-01, 04-01, 05-01, 06-01 SUMMARY.md files

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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