Two compilers that walk a graph the same way walk it through one emitter (#85)

Refactoring round two: the particle and shader compilers share emitGraph.ts (cycle detection,
duplicate names, emit order) and keep only their rules. FontLibrary and TextureLibrary sit on
FileLibrary (base URL, loading/failed bookkeeping, listeners); SoundLibrary keeps its own
contract. The three Create*Command share ImportFileCommand, the three renames share
RenameCommand - class names stay. bandBounds() in framing.ts and portNameField() in
portSection.ts replace in-file clones, and three comments that told history now state the rule.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/graph/GraphInterpreter.ts

@@ -19,8 +19,8 @@ const MAX_STEPS_PER_FIRE = 100_000;
 
 /**
  * How far exec edges may nest. The interpreter recurses along them, so this is what keeps a flow
- * feeding back into itself off the call stack – a job the step budget can no longer do now that a
- * legitimate pulse may run tens of thousands of steps.
+ * feeding back into itself off the call stack – the step budget cannot, since a legitimate pulse
+ * may run tens of thousands of steps.
  */
 const MAX_DEPTH = 1000;