bump machineGroupControl: governance + unit-self-describing demand (26e92b5)

MGC submodule lands the 2026-05-14 governance review fixes plus rolled-up
session work: _output-manifest.md per the new output-coverage rule,
computeEqualFlowDistribution extracted as a pure function (testable without
MGC), groupEfficiency degenerate-case fix, unit-self-describing set.demand,
eta = (Q*dP)/P formula correction, and dashboard fan-out hardening
(auto-init, NCog normalization, Q-H trim, null-trap closure). Suite 108/108.

Superproject adds:
- .claude/rules/output-coverage.md: every-output-every-state testing rule
  prompted by the eta-null crash earlier in the session.
- CLAUDE.md: pointer to the new rule under Conventions.

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

CLAUDE.md

@@ -27,6 +27,7 @@ Each node follows a three-layer pattern:
 - Tick loop runs at 1000ms intervals for time-based updates
 - Output ports + 3-tier architecture: see `.claude/rules/node-architecture.md`
 - **Multi-tab demo flows**: see `.claude/rules/node-red-flow-layout.md` for the tab/link-channel/spacing rule set used by `examples/`
+- **Output coverage** (every output, every state, every layer): see `.claude/rules/output-coverage.md` — manifest + populated/degraded tests are mandatory for any change that touches Port 0/1/2 keys, function-node fan-outs, telemetry fields, or dashboard widget sources
 
 ## Development Notes
 - No build step required - pure Node.js