docs(readme): collapse Scope section — strip CHANGELOG duplicate + internal refs

The Scope section had grown to 556 lines (60% of the README, ~4400
words) carrying a near-complete per-milestone narrative duplicating
CHANGELOG.md — which the section itself cross-referenced at the end
"for the per-release contract." Beyond the duplication it violated
the project's `feedback_public_docs_clean` directive across hundreds
of internal references that mean nothing to a CLI user:

- Milestone refs (M8, M19, M28, v0.7-M42, v0.6-M38 D6, Decision 11)
- Design-doc section refs (§5.8, §6.1, cli-design §11.5, D1 closure)
- R-class refactor tracking (R-v0.5-NEW-18, D10 closure, D11)
- Wire op names (add_file_to_column, change_team_memberships,
  move_item_to_board, BoardDuplication, set_item_description_content,
  duplicate_board_with_pulses, etc.)
- Stale framing on the M40 deferral — the section still carried the
  "paid-tier gating + opaque INTERNAL_SERVER_ERROR { service:
  'docs-api' }" wording that the 2026-05-22 dev-board probe refuted
  (M40 is feature-real on multi_level boards; user-memory
  project_m40_findings_deferred flags this correction)

This is the same surface R-v0.9-NEW-15 flagged at the post-publish
refactor-audit ("README Scope-section drift at release-prep"); the
audit fixed the LITERAL "v0.8.0 (current)" mislabel but didn't
restructure.

Replace with two short blurbs — v0.9.0 (current) headline capability
+ "What's next" roadmap headlines — both linking to CHANGELOG.md
(per-release history) and docs/cli-design.md §13 (full roadmap). All
per-milestone detail stays in CHANGELOG.md where it already lives;
no information lost. Aligns the public README with the same
discipline source-level help strings adopted at v0.8 release-prep.

Net 925 → 396 lines (-553 / +24).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Nick Webster