Let a node read another node's geometry and a text's measurements #328

Part of #326. Batch 2 — depends on #327.

Nothing in a scenario can refer to anything else in it. Eight lines joining a logo to badges orbiting around it were abandoned during the rebuild, because a line's endpoint cannot follow a node whose position is animated. A ? detaching from the end of a typed sentence was abandoned for the same reason: there is no way to ask where that sentence ends.

Glyph positions are already computed at paint time in engine/renderer/text.rs (str_to_glyphs_vec, get_widths, then a positions vector). They are simply never exposed. This workstream is mostly exposure, not new geometry.

Owned files

• crates/rustmotion-core/src/engine/deps.rs (new — the dependency graph)
• crates/rustmotion-core/src/engine/layout_pass.rs, paint_pass.rs
• crates/rustmotion-core/src/engine/renderer/text.rs (retain and expose the glyph run)
• crates/rustmotion-components/src/intrinsic.rs

Do NOT write: crates/rustmotion-core/src/expr/** (#327 owns the evaluator; add reference resolution as a resolver it calls).

Deliverables

1. A node takes an optional id, unique within its scene. An expression then reads @id.prop.

2. Four families of readable property.

   Family	Properties	Resolved
   Geometry	x y width height cx cy right bottom	after layout_pass
   Animated transform	tx ty scale rotation opacity	per frame
   Text measurement	textWidth capHeight ascender baseline	after layout_pass
   Glyphs	glyph(n).x, glyph(n).cx, glyphCount	after layout_pass

   The animated-transform family is the one that carries the architectural cost, and it is the one the eight lines need.

3. A dependency graph built once at load and topologically sorted. Static references resolve in a pass after layout_pass. Animated references resolve per frame, in topological order rather than tree order. Getting this wrong yields values one frame stale, which is invisible until someone pauses, so the ordering needs a test that would catch exactly that.

4. Errors — a cycle is reported at load with the full chain, named and located. A reference crossing a scene boundary is reference_cross_scene and is rejected, since scenes are independent render units.

5. The detaching glyph needs no glyph slicing. The author writes the sentence without its last character and places a separate node at "x": "= @q.right" with its own animation. glyph(n) remains for per-letter work the char_* presets do not cover.

Acceptance

• A line whose x2 is "= @chip3.cx + @chip3.tx" tracks an orbiting badge across every frame, with no one-frame lag
• A cycle A -> B -> A fails at load naming both nodes
• text.caret still works unchanged; it already covers the caret case and is not re-implemented here