Add wiki/ folder with functional description + draw.io diagrams

Moves documentation into the code repo so code, docs, and diagrams
version-lock and review together. Previous location was
pumpingStation.wiki.git; that will shrink to a pointer.

Contents:
- wiki/README.md — doc index
- wiki/functional-description.md — operator-facing reference derived
  from src/specificClass.js: basin model, net-flow selection,
  level-based control zones, safety interlocks, registration topology
- wiki/diagrams/ — editable draw.io sources paired with SVG exports
  (basin-model, control-zones, safety-rules) + README with the
  open/edit/export/commit workflow

The .drawio files are rough starters; iterate in draw.io and re-export.

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

wiki/diagrams/safety-rules.drawio.svg

@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 900 620" font-family="Arial, sans-serif" font-size="13">
+  <title>Safety rules — asymmetric by direction</title>
+
+  <text x="450" y="30" text-anchor="middle" font-weight="bold" font-size="16">Safety rules — asymmetric by direction</text>
+
+  <!-- DRY-RUN box -->
+  <rect x="80" y="80" width="340" height="340" fill="#FFF3E0" stroke="#E65100" stroke-width="2" />
+  <text x="250" y="112" text-anchor="middle" font-weight="bold" font-size="14">DRY-RUN</text>
+  <text x="250" y="130" text-anchor="middle" font-size="13" fill="#6F4A19">(direction = draining)</text>
+
+  <text x="100" y="162" font-size="13">upstream children  —  <tspan font-weight="bold">KEEP</tspan></text>
+  <text x="100" y="188" font-size="13" fill="#E65100">downstream children  —  <tspan font-weight="bold">STOP</tspan></text>
+  <text x="100" y="214" font-size="13" fill="#E65100">machineGroups  —  <tspan font-weight="bold">STOP</tspan></text>
+  <text x="100" y="240" font-size="13" fill="#E65100">control loop  —  <tspan font-weight="bold">BLOCKED</tspan></text>
+
+  <line x1="100" y1="268" x2="400" y2="268" stroke="#E65100" stroke-dasharray="3 3" />
+  <text x="100" y="294" font-size="12" font-style="italic">safetyControllerActive = true</text>
+  <text x="100" y="316" font-size="12" font-style="italic">Pumps must stop before sucking air.</text>
+
+  <!-- OVERFILL box -->
+  <rect x="480" y="80" width="340" height="340" fill="#FFEBEE" stroke="#C62828" stroke-width="2" />
+  <text x="650" y="112" text-anchor="middle" font-weight="bold" font-size="14">OVERFILL</text>
+  <text x="650" y="130" text-anchor="middle" font-size="13" fill="#7A1919">(direction = filling)</text>
+
+  <text x="500" y="162" font-size="13" fill="#C62828">upstream children  —  <tspan font-weight="bold">STOP</tspan>  ⚠</text>
+  <text x="500" y="188" font-size="13">downstream children  —  <tspan font-weight="bold">KEEP</tspan></text>
+  <text x="500" y="214" font-size="13">machineGroups  —  <tspan font-weight="bold">KEEP</tspan></text>
+  <text x="500" y="240" font-size="13">control loop  —  <tspan font-weight="bold">ACTIVE</tspan></text>
+
+  <line x1="500" y1="268" x2="800" y2="268" stroke="#C62828" stroke-dasharray="3 3" />
+  <text x="500" y="294" font-size="12" font-style="italic">Level control keeps commanding downstream MGC.</text>
+  <text x="500" y="324" font-size="12" font-style="italic" fill="#C62828">⚠ "upstream STOP" is only correct in a cascaded layout.</text>
+  <text x="500" y="342" font-size="12" font-style="italic" fill="#C62828">In a gravity-sewer station the inflow can't be</text>
+  <text x="500" y="360" font-size="12" font-style="italic" fill="#C62828">stopped — log the spill instead.</text>
+
+  <!-- Triggers block -->
+  <text x="80" y="470" font-weight="bold" font-size="13">Triggers (either condition fires the rule):</text>
+  <text x="100" y="498" font-size="12">• vol &lt; triggerLowVol     (triggerLowVol  = minVol × (1 + pct/100))</text>
+  <text x="100" y="520" font-size="12">• vol &gt; triggerHighVol    (triggerHighVol = maxVolOverflow × pct/100)</text>
+  <text x="100" y="542" font-size="12">• remainingTime &lt; timeleftToFullOrEmptyThresholdSeconds (if enabled)</text>
+</svg>