Phase 5: group-voice docs, onboarding runbook, CHORUS icon — v2.0.0-rc.1

The final phase of CHORUS-PLAN.md. Code- and doc-complete for group use;
rc pends live deployment at chorusapi.mpm.to.

- Repo README rewritten for CHORUS: group model (schema 5), concurrency
  posture, configuration, baked-build onboarding, layout, testing, 2.0
  version history (ECHO history referenced at the fork tag).
- Operator→member voice sweep across SKILL.md (incl. the trigger
  description, now group-aware), all references, 8 command docs, plugin
  README; member preferences / semantic layer / triage guidance describe
  the group model.
- docs/ONBOARDING.md: member runbook — vault stand-up, per-member config,
  bake, deliver, self-onboarding first load, norms, offboarding.
- docs/USAGE.md rewritten as the member usage guide.
- New icon: chorus-icon.svg + 1024/512/64 PNGs (three voices, one center).
- Removed ECHO-era assets (icons, spec PDF, perf briefs); ECHO planning
  docs retired to docs/history/. All preserved at echo-fork-point.
- eval/README documents test_multimember.py. Manifest -> 2.0.0-rc.1;
  rebuilt chorus-memory.plugin.

Verified: routing-sync, 25/25 unit, scaffold, 5 mock e2e suites,
run_eval metrics green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

chorus-icon.svg

@@ -0,0 +1,33 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1024 1024" width="1024" height="1024">
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="1" y2="1">
+      <stop offset="0" stop-color="#141433"/>
+      <stop offset="1" stop-color="#232355"/>
+    </linearGradient>
+  </defs>
+  <!-- background -->
+  <rect x="0" y="0" width="1024" height="1024" rx="224" fill="url(#bg)"/>
+  <!-- three voices: overlapping wave arcs radiating from three offset origins -->
+  <g fill="none" stroke-linecap="round">
+    <!-- voice 1 — teal -->
+    <g stroke="#3fd8c2">
+      <circle cx="392" cy="452" r="70"  stroke-width="34" opacity="0.95"/>
+      <circle cx="392" cy="452" r="160" stroke-width="26" opacity="0.55"/>
+      <circle cx="392" cy="452" r="250" stroke-width="20" opacity="0.28"/>
+    </g>
+    <!-- voice 2 — violet -->
+    <g stroke="#8f7bff">
+      <circle cx="632" cy="452" r="70"  stroke-width="34" opacity="0.95"/>
+      <circle cx="632" cy="452" r="160" stroke-width="26" opacity="0.55"/>
+      <circle cx="632" cy="452" r="250" stroke-width="20" opacity="0.28"/>
+    </g>
+    <!-- voice 3 — amber -->
+    <g stroke="#ffb347">
+      <circle cx="512" cy="640" r="70"  stroke-width="34" opacity="0.95"/>
+      <circle cx="512" cy="640" r="160" stroke-width="26" opacity="0.55"/>
+      <circle cx="512" cy="640" r="250" stroke-width="20" opacity="0.28"/>
+    </g>
+  </g>
+  <!-- shared center where the three voices meet -->
+  <circle cx="512" cy="512" r="46" fill="#f4f2ff"/>
+</svg>