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/doc/src/document.rs

@@ -1128,6 +1128,10 @@ pub struct Document {
     /// Bodies moved into another component than their feature's (by body name).
     #[serde(default, skip_serializing_if = "std::collections::BTreeMap::is_empty")]
     pub body_components: std::collections::BTreeMap<String, u64>,
+    /// Bodies moved into another component keep their place in the world: the transform from
+    /// the new component's frame to the frame the body was made in (by body name).
+    #[serde(default, skip_serializing_if = "std::collections::BTreeMap::is_empty")]
+    pub body_offsets: std::collections::BTreeMap<String, crate::Mat>,
     /// Browser groups (folders of bodies, sketches or construction planes).
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub browser_groups: Vec<BrowserGroup>,
@@ -1196,6 +1200,7 @@ impl Document {
             configs: Default::default(),
             parts: Default::default(),
             body_components: Default::default(),
+            body_offsets: Default::default(),
             materials: Default::default(),
             appearances: Default::default(),
             favorites: Default::default(),