Tools: Convert Point tool in the Pen flyout (#3204) (#3211)

Convert Point is a tool of its own, built on the existing path.convertPoint
edit that Pen + Alt already drives. A click makes a smooth anchor a corner, a
drag from an anchor pulls out smooth handles, a drag on a handle moves it
alone. The tool selects the anchor it converts so its handles show; a press on
empty canvas or a segment does nothing, and Cmd/Ctrl is Direct Selection, as
with the Pen. It shares the Pen's key (P).

Original glyph with an ATTRIBUTION.md row; tool name in all catalogs; README
tool list and the G6 / ui-parity / roadmap counts updated (tools 56 of 68, the
earlier 53 was stale).

Co-authored-by: Brandon Thomas <echelon@gmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

assets/icons/convert-point.svg

@@ -0,0 +1,16 @@
+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  viewBox="0 0 24 24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <!-- PhotoCraft's own Convert Point glyph: a corner point, an angle with a square anchor on its apex. -->
+  <rect x="9.75" y="4.75" width="4.5" height="4.5" />
+  <path d="M10.5 9.25 4 19" />
+  <path d="M13.5 9.25 20 19" />
+</svg>