Components are frames (user bug #4)

What a component holds moves with its occurrence, and picks in the world land in the
component's frame:
- Sketches and construction planes show where their component is placed (free move, joint
  drive, Capture Position); sketch.inspect reports sketch points in the world.
- frames.rs maps a command's world picks into the frame of the body they lie on (through the
  inverse of its placement: a moved component or a pasted instance), points that make new
  geometry into the active component's frame, and directions with them; instance body names
  ("Body1 (Pin:2)") become the component's body. Fillet/chamfer edges, shell/offset/draft
  faces, face extrude/revolve, sketch on face, holes, sheet metal and plastic picks, primitives,
  appearance faces, analyses. Once per command (not again for commands run by commands); the
  active-frame fallback stays for commands without a table. Nothing changes while every
  placement is the identity.
- component.move_bodies keeps a body where it is in the world (Document.body_offsets: from the
  new component's frame to the one it was made in; renames and deleted components follow).
- The UI reads the placed model (Session::world_state) for display, picking, sketch editing and
  dialogs; live previews use it once anything is placed.
Tests (engine): sketches and construction planes move (and turn) with the component; world
picks fillet, sketch, hole and make boxes in a moved component; a pick on a pasted instance;
move_bodies keeps the world place there and back; a sketch on a face follows a Move feature.
QA's s34 now runs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/engine/src/lib.rs

@@ -9,6 +9,7 @@
 #![forbid(unsafe_code)]
 
 pub mod cmd;
+pub mod frames;
 pub mod params;
 pub mod recovery;
 pub mod sample;
@@ -297,6 +298,11 @@ impl Session {
         let before = Snapshot { label: spec.label.to_string(), doc: self.doc.clone(), active_sketch: self.active_sketch };
         let null = Value::Object(Default::default());
         let params = if params.is_null() { &null } else { params };
+        // Picks in the world go into their component's frame (once: commands run by commands
+        // already have them there).
+        let (_nested, outermost) = frames::Nested::enter(spec.id);
+        let mapped = if outermost { frames::to_local(self, spec.id, params) } else { None };
+        let params = mapped.as_ref().unwrap_or(params);
         let r = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| (spec.run)(self, params)));
         let r = match r {
             Ok(r) => r,