test: add pcb snapshot test for polygon smtpads with solder mask coverage

Adds a PCB snapshot test demonstrating polygon-shaped smtpads with
coveredWithSolderMask in a 5-segment capacitive touch slider layout.

The test verifies:
- 5 diamond-shaped polygon pads created correctly
- All pads have is_covered_with_solder_mask: true
- No solder paste generated for solder-mask-covered pads
- Visual PCB snapshot for regression detection

Relates to tscircuit/tscircuit#786

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

Author: TheAuroraAI

tests/components/normal-components/polygon-smtpad-with-soldermask.test.tsx

@@ -0,0 +1,69 @@
+import { test, expect } from "bun:test"
+import { getTestFixture } from "tests/fixtures/get-test-fixture"
+
+/**
+ * Snapshot test for polygon-shaped smtpads with solder mask coverage.
+ *
+ * Demonstrates using polygon smtpads to create a 5-segment capacitive touch
+ * slider footprint — a common use case where pads must be covered with solder
+ * mask so the finger is insulated from direct electrical contact.
+ *
+ * Relates to: https://github.com/tscircuit/tscircuit/issues/786
+ */
+test("polygon smtpad with soldermask - capacitive touch slider", () => {
+  const { project } = getTestFixture()
+
+  const segmentCount = 5
+  const spacing = 3.0 // mm between segment centers
+
+  // Diamond-shaped polygon points (relative to pad center)
+  const diamondPoints = (hw: number, hh: number) => [
+    { x: 0, y: hh },
+    { x: hw, y: 0 },
+    { x: 0, y: -hh },
+    { x: -hw, y: 0 },
+  ]
+
+  project.add(
+    <board width="22mm" height="12mm">
+      <chip
+        name="U1"
+        footprint={
+          <footprint>
+            {Array.from({ length: segmentCount }, (_, i) => {
+              const cx = (i - Math.floor(segmentCount / 2)) * spacing
+              return (
+                <smtpad
+                  key={i}
+                  shape="polygon"
+                  layer="top"
+                  pcbX={cx}
+                  pcbY={0}
+                  portHints={[`pin${i + 1}`]}
+                  coveredWithSolderMask
+                  points={diamondPoints(1.2, 1.8)}
+                />
+              )
+            })}
+          </footprint>
+        }
+      />
+    </board>,
+  )
+
+  project.render()
+
+  // Verify all 5 pads have solder mask coverage set
+  const pads = project.db.pcb_smtpad.list()
+  expect(pads).toHaveLength(segmentCount)
+  for (const pad of pads) {
+    expect(pad.is_covered_with_solder_mask).toBe(true)
+    expect(pad.shape).toBe("polygon")
+  }
+
+  // Verify no solder paste is generated for solder-mask-covered pads
+  expect(project.db.pcb_solder_paste.list()).toHaveLength(0)
+
+  // Visual PCB snapshot
+  expect(project).toMatchPcbSnapshot(import.meta.path)
+})