Graph: optionales Grid-Snapping beim Ziehen von Nodes

Ein Toggle in der Graph-Kopfzeile lässt gezogene Nodes auf dem 24er-Raster
einrasten – derselben Größe, die den Hintergrund zeichnet. Einschalten bewegt
nichts; die Regel greift erst beim nächsten Zug. Bei Mehrfachauswahl richtet
sich jeder Node für sich aus, statt einem gemeinsamen Versatz zu folgen, der
die alten krummen Abstände mitschleppen würde.

Die Entscheidung liegt als reine Funktion in framing.ts, wo die übrige
Graph-Geometrie schon wohnt, und ist dort wie im Browser gepinnt.

README.md

@@ -252,6 +252,11 @@ shown on the node and editable in the inspector.
   **Add node…** (the palette, dropping the node in the middle of the view – the right-click nobody
   finds), **Fit** (which zooms out far enough to hold every node, measuring each by its own drawn
   height – `editor/framing.ts`), and the size of the graph as "N nodes · M links".
+- **Snap** (header checkbox, off by default): a drag drops each node it carries on the nearest
+  24 px grid line – the same grid the background draws. It takes effect on the next drag only, so
+  switching it on never shuffles a graph that is already laid out, and a node nobody drags never
+  moves. Every node of a selection snaps **for itself**, so dragging a group is how you line one
+  up; the offset is a decision about rectangles and lives with the others in `editor/framing.ts`.
 - **Selection-following, not selection-bound**: selecting a behavior asset, a placed behavior
   or one of its nodes shows that graph; a selection about anything else (a sprite, nothing at
   all) leaves the tab on the behavior you were editing, because checking a sprite's position
@@ -599,7 +604,7 @@ npm run check        # typecheck + lint + format:check + tests, what CI would ru
                      #   code is lost (tail's is reported), so a red run reads as green
 npm run build        # writes dist/ and regenerates index.html
 export GM_REMOTE=user@host                                    # optional: run the browser elsewhere; see below
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 483 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 491 editor checks, screenshots in /tmp/gm-e2e-*.png
 GM_STEPS=20 node tools/e2e.mjs                                # or 1-12, or 6,20 – a subset while working on one step
 ./e2e.sh start [GM_STEPS]                                     # the same run detached, see below
 ./e2e.sh status                                               # live progress, or the last run's result