Rename eval/ → simulations/ and fix log-write bug

Per discussion: "test" and "eval" overlap in meaning; "simulations"
is more honest about what's actually happening — scripted plant
inputs driving a physics sim, then recorded for analysis.

Rename scope:
- eval/ → simulations/ (tracked as git renames)
- Internal references in run.js and README.md updated
- wiki/modes/mpc.md link updated

Also fixes a log-write bug noticed during the rename:
- run.js didn't mkdir simulations/logs/ before createWriteStream,
  so the stream opened into a potentially non-existent dir and the
  file never materialised. Added fs.mkdirSync(..., recursive:true).
- end() wasn't awaited, so the process could exit before the stream
  flushed. Now awaits the 'finish' event. Confirmed: 1200 records
  actually land in simulations/logs/<scenario>.jsonl.
- Added simulations/logs/.gitignore so future JSONL artefacts stay
  out of the repo but the dir remains tracked.

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

simulations/scenarios/levelbased-steady.js

@@ -0,0 +1,60 @@
+// Steady sewer inflow, level-based control, pumps should settle.
+//
+// Expectation: with a stable inflow of 0.008 m³/s and a pump bank with
+// max capacity 0.012 m³/s, the level settles in the RAMP zone (between
+// startLevel and maxLevel) at roughly the point where demand matches
+// inflow. No safety trips should fire.
+
+module.exports = {
+  name: 'levelbased-steady',
+  description: 'Constant sewer inflow below pump capacity; level converges inside the RAMP zone with demand matching inflow.',
+  durationSec: 1200,
+
+  config: {
+    general: { name: 'EvalSteady', id: 'eval-steady', unit: 'm3/h',
+      logging: { enabled: false, logLevel: 'error' } },
+    functionality: { softwareType: 'pumpingStation', role: 'stationcontroller', positionVsParent: 'atEquipment' },
+    basin: { volume: 50, height: 5, inflowLevel: 3, outflowLevel: 0.2, overflowLevel: 4.5 },
+    hydraulics: { refHeight: 'NAP', basinBottomRef: 0, minHeightBasedOn: 'outlet' },
+    control: {
+      mode: 'levelbased',
+      allowedModes: new Set(['levelbased']),
+      levelbased: { minLevel: 1, startLevel: 2, maxLevel: 4 },
+    },
+    safety: {
+      enableDryRunProtection: true,
+      dryRunThresholdPercent: 2,
+      enableOverfillProtection: true,
+      overfillThresholdPercent: 98,
+      timeleftToFullOrEmptyThresholdSeconds: 0,
+    },
+  },
+
+  setup: async (ps) => {
+    // Stub MGC: its pumps collectively deliver (demand/100) × MAX_OUTFLOW.
+    const MAX_OUTFLOW = 0.012;  // m³/s
+    ps.machineGroups['mgc1'] = {
+      config: { general: { name: 'mgc1' } },
+      turnOffAllMachines: () => {
+        ps.measurements.type('flow').variant('predicted').position('out').child('mgc1').value(0, Date.now(), 'm3/s');
+      },
+      handleInput: async (_source, demand) => {
+        const d = Math.max(0, Math.min(100, Number(demand) || 0));
+        const outflow = (d / 100) * MAX_OUTFLOW;
+        ps.measurements.type('flow').variant('predicted').position('out').child('mgc1').value(outflow, Date.now(), 'm3/s');
+      },
+    };
+    ps.calibratePredictedLevel(2.0);  // start at the bottom of the RAMP zone
+  },
+
+  inputs: (t, ps) => {
+    ps.setManualInflow(0.008, Date.now(), 'm3/s');  // ≈ 29 m³/h
+  },
+
+  expectations: [
+    { name: 'no safety trips', type: 'safety_trips_eq', value: 0 },
+    { name: 'level stays below overflow', type: 'max_level_bounded', value: 4.5 },
+    { name: 'level stays above outflow', type: 'min_level_bounded', value: 0.2 },
+    { name: 'no threshold issues on init', type: 'threshold_issues_eq', value: 0 },
+  ],
+};