feat(commands): add FLATSHOT and CONVTOSURFACE

- FLATSHOT: project the selected solid's edges to 2D Line entities at Z=0
- CONVTOSURFACE: convert the selected solid(s) to Surface entities

Both reuse the cached B-rep's edge wires. COMMANDS.md: 219/262.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/commands/mod.rs

@@ -346,6 +346,8 @@ inventory::submit!(crate::command::CommandRegistration {
         "REG",
         "ARCHIVE",
         "ETRANSMIT",
+        "FLATSHOT",
+        "CONVTOSURFACE",
         // Slice/section + interference + press-pull/thicken + 3D transforms + wall/pyramid.
         "SLICE",
         "SL",