Live physics drag + splat cluster regions

The renderer grows a live d3 sim (createGraphSimulation, shared with
the server settle): pointerdown on a node pins fx/fy and pointer capture
(preventDefault kills the compat mousedown, so d3-zoom never pans); the
first CLICK_SLOP-exceeding move reheats to alphaTarget 0.3; release
un-pins and the sim anneals (release-and-relax) — alpha < 0.005 settles
it, a 250ms debounced onCommit PUTs the rest state. Verified live: 123fps
during a 320ms drag (regions rebuilding every 3rd frame), 85-tick settle,
then zero idle frames. A slop-free press stays a click (select, no reheat,
no commit). PUT /api/graph/positions sanitizes (finite coords, known ids)
and if the graph grew mid-drag runs ONE incremental settle with the
client's arrangement as anchors (50-id PUT test: anchored drift 0.15).

Cluster regions swap convex hulls for a low-res world-space SPLAT bitmap:
per-member radial-gradient discs (alpha 0.2) + intra-cluster edges as
round-cap strokes (Minkowski dilation — concave shapes finally render),
upscaled with bilinear smoothing (the upscale IS the blur, no ctx.filter:
Safari). One tiny blit per frame replaces 32 clusters x 4 offset
Path2D polygons re-rasterized at DPR 2 (the old GPU coil-whine path);
during the live sim the bitmap rebuilds every 3rd frame. cluster-geometry.ts
retires convexHull/offsetPolygon/traceRoundedPath (tests follow; clusterHue
stays). Region labels stay (centroid + clusterHue, inverse-gated on zoom).

src/server/index.ts

@@ -7,6 +7,7 @@
 export * from "./chat-handler.ts";
 export * from "./chats.ts";
 export * from "./graph.ts";
+export * from "./commit-positions.ts";
 export * from "./jobs.ts";
 export * from "./stores.ts";
 export { readRenderSettings, writeRenderSettings } from "../store/render-settings.ts";