Sheet metal: tear as a fourth corner relief shape (#809)

A sheet metal rule's corner relief shape can now be tear; saved under format 17 with a note.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/tests/scenarios/s51_sheet_metal_corner_relief.json

@@ -1,6 +1,6 @@
 [
  {
-  "note": "Sheet Metal Rules: the Corner Relief Shape row sets the rule's corner_relief_shape, and the tray made with the rule follows. The bend on the 120 mm edge is 120 - 2*s0 long (s0 = 3*tan 36 deg) and 8 mm shorter with a relief 8 mm across at both its ends."
+  "note": "Sheet Metal Rules: the Corner Relief Shape row sets the rule's corner_relief_shape, and the tray made with the rule follows. The bend on the 120 mm edge is 120 - 2*s0 long (s0 = 3*tan 36 deg) and 8 mm shorter with a relief 8 mm across at both its ends. Torn, its centre line is sin 72 deg - 0.5/sqrt 2 longer: each end runs half that past the corner, toward its flange's closed end."
  },
  {
   "call": "ui.set",
@@ -213,5 +213,53 @@
  },
  {
   "shot": "s51_rectangular_reliefs"
+ },
+ {
+  "start": "sheet.manage_rules"
+ },
+ {
+  "click": {
+   "handle": "dialog:Corner Relief Shape"
+  }
+ },
+ {
+  "click": {
+   "handle": "dialog:Corner Relief Shape:Tear"
+  }
+ },
+ {
+  "widget": "OK"
+ },
+ {
+  "expect": {
+   "dialog": null,
+   "errors": 0,
+   "query": {
+    "command": "sheet.rules",
+    "path": [
+     "rules",
+     0,
+     "rule",
+     "corner_relief_shape"
+    ],
+    "value": "tear"
+   }
+  }
+ },
+ {
+  "expect": {
+   "query": {
+    "command": "sheet.flat_pattern",
+    "path": [
+     "bends",
+     0,
+     "length"
+    ],
+    "value": 116.238247958
+   }
+  }
+ },
+ {
+  "shot": "s51_torn_corners"
  }
 ]