docs: fixit pass for consistency now that M3 is closed

[DeDuva]

Summary

A documentation consistency pass across the repo now that M3 (#70) and the
roadmap-consolidation PR just before it (#69) are both merged. No scope or
narrative changes — every edit corrects something that had drifted out of
sync with a merged PR, with the evidence for the correction cited inline.

• README.md / docs/ecosystem.md — both still described
  docs/pragmatic_mvp.md as holding "the status ledger." Give the roadmap one home, and make CLAUDE.md point at the real plan #69 moved that to
  ROADMAP.md. Added ROADMAP.md to README's document table; pointed
  ecosystem.md's plan table at it.
• docs/m3-readiness-review.md / docs/pragmatic_mvp.md — the M3 progress
  sections still said arms 2 and 3 were outstanding / not run. Updated to
  the landed state (M3-5: run arm 2 (three-way agent cost comparison) — closes M3 #70), and folded the M3-5 arms into the same bulleted
  list format as M3-0..M3-6 instead of a trailing paragraph.
• docs/ecosystem.md — the Harbor-track pause note was stale: squad's
  own ROADMAP.md records the pause lifted 2026-08-08. Corrected, and
  distinguished from the still-open cross-track gate (which needs Harbor
  at its own M8, not this).
• docs/ecosystem.md — the stats-bridge "Watch out" block described a
  working-copy sys.path hack that predates the fix duva-bench's own
  PLAN.md documents landing 2026-08-08. Replaced with the current setup,
  plus a real trap found in its place while running M3-5 arm 3: a stale or
  half-built local venv (no pyvenv.cfg) silently reads as "just rerun
  setup-stats.sh," not as a report-generation failure worth investigating.
• docs/ecosystem.md — issues payload is documented optional and is NOT NULL in the database #63 and The native plane cannot open a run on its own — undocumented dependency on the compat plane #65, linked as open findings, are
  both closed; The native plane cannot open a run on its own — undocumented dependency on the compat plane #65 became docs/api-compatibility.md's "Plane
  dependencies" section. Only No native-plane response has a schema — all 87 operations type requests only #64 is still open.
• docs/api-compatibility.md — extended "Plane dependencies" with the
  candidate-set analogue of The native plane cannot open a run on its own — undocumented dependency on the compat plane #65's intent-minting gap: the native MCP
  surface has no proposal-open tool, so a candidate set's proposal has to
  be opened via one compat-plane REST call. Confirmed directly while
  running M3-5 arm 2 (M3-5: run arm 2 (three-way agent cost comparison) — closes M3 #70) — the adp-mcp trials needed exactly this.

Test plan

• make check-docs passes (CLAUDE.md path assertions unaffected —
  no paths named there were touched)
• make check full suite green
• Every new/changed relative link verified to resolve to a real file