docs(plan): record M016 evidence deviation and complete milestone

docs/3d/maze32-command-chamber/masks/north-arrival-cutter.json

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+{
+  "id": "north-arrival",
+  "shape": "rectangular-door",
+  "centerMeters": [0, 5.85, 1.55],
+  "dimensionsMeters": [3.0, 0.8, 3.1],
+  "wall": "north",
+  "operation": "EXACT_BOOLEAN_DIFFERENCE"
+}

docs/3d/maze32-command-chamber/masks/north-arrival-mask.svg

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+<svg xmlns="http://www.w3.org/2000/svg" width="600" height="400" viewBox="0 0 600 400"><rect width="600" height="400" fill="white"/><rect x="150" y="60" width="300" height="310" fill="black"/><path d="M150 370V60H450V370" fill="none" stroke="#777" stroke-width="4"/><text x="300" y="35" text-anchor="middle" font-family="sans-serif" font-size="20">north-arrival: 3.0 m × 3.1 m</text></svg>

docs/3d/maze32-command-chamber/masks/opening-contact-sheet.svg

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+<svg xmlns="http://www.w3.org/2000/svg" width="900" height="560" viewBox="0 0 900 560"><rect width="900" height="560" fill="white"/><text x="40" y="48" font-family="sans-serif" font-size="26" fill="black">Opening mask contact sheet</text><rect x="80" y="110" width="330" height="340" fill="#111"/><path d="M80 450V110H410V450" fill="none" stroke="#777" stroke-width="5"/><text x="245" y="495" text-anchor="middle" font-family="sans-serif" font-size="22">north-arrival · door · 3.0 × 3.1 m</text><text x="500" y="170" font-family="sans-serif" font-size="20" fill="black">Cutter: rectangular Exact Boolean</text><text x="500" y="210" font-family="sans-serif" font-size="20" fill="black">Wall: north</text><text x="500" y="250" font-family="sans-serif" font-size="20" fill="black">Passage depth: 0.8 m</text><text x="500" y="290" font-family="sans-serif" font-size="20" fill="black">Destination: entry apron</text></svg>