Add physical dimensions to bin editor for correct aspect ratio

When de-perspectiving a bin photo taken at an angle, inferring the
output size from the quadrilateral shape squishes the result. Entering
real-world W×H (mm) lets the server use the correct aspect ratio,
scaled to the same resolution as the inferred size.

- Bin editor dialog: W×H number inputs, pre-filled from saved phys_w/phys_h
- PUT /api/bins/:id/corners: accepts optional phys_w/phys_h; when provided,
  derives bin_w/bin_h from the physical aspect ratio at equivalent area
- phys_w/phys_h stored on the bin record for re-use on next edit
- future-plans.md: bin types note (reusable dimensions per model)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/templates.html

@@ -656,6 +656,15 @@
 			<label>Name</label>
 			<input type="text" id="bin-editor-name" autocomplete="off">
 		</div>
+		<div class="form-row">
+			<label>Dimensions (mm)</label>
+			<div class="bin-editor-dims">
+				<input type="number" id="bin-editor-width" placeholder="W" min="1" step="1">
+				<span>×</span>
+				<input type="number" id="bin-editor-height" placeholder="H" min="1" step="1">
+				<span class="form-hint">Leave blank to infer from corners</span>
+			</div>
+		</div>
 		<canvas id="bin-editor-canvas" class="bin-editor-canvas"></canvas>
 		<div class="dialog-actions">
 			<button type="button" class="btn btn-secondary" id="bin-editor-cancel">Cancel</button>