Re-tune render sizes for the world-space model: smaller defaults, wide low ends

The defaults were calibrated in the screen-fixed era; world-scaling renders
sizes at setting x k/kFit, so at the default label gate (2x fit) everything
read ~2x too big ("labels way too large even at the minimum"). Fit-zoom
normalizes layout scale away, so the fix belongs in sizes, not layout:
spreading nodes further apart in world units changes nothing at fit.

- Defaults: nodeSize 6 -> 4, arrowLength 5 -> 4, labelSize 12 -> 7.
- Clamps/slider ranges widened at the low end: nodeSize 1-14 (step 0.5),
  edgeWidth 0.25-4 (step 0.25), arrowLength 1-15 (step 0.5),
  labelSize 3-24 (step 0.5).
- GLOW_PAD 9 -> 6 (halo dominated small discs), REGION_LABEL_SIZE 18 -> 14.
- Tests updated for the new clamp bounds plus a low-end pass-through case
  (403/403). The saved render-settings.json still shadows defaults by
  design; the local copy was reset so the new defaults showed immediately.

components/graph-view.tsx

@@ -500,33 +500,33 @@ export function GraphView() {
 						<div className="mt-1.5 flex flex-col gap-2 border-t pt-1.5">
 							<SettingSlider
 								label="Node size"
-								min={2}
+								min={1}
 								max={14}
-								step={1}
+								step={0.5}
 								value={settings.nodeSize}
 								onChange={(v) => changeSettings((cur) => ({ ...cur, nodeSize: v }))}
 							/>
 							<SettingSlider
 								label="Edge width"
-								min={0.5}
+								min={0.25}
 								max={4}
-								step={0.5}
+								step={0.25}
 								value={settings.edgeWidth}
 								onChange={(v) => changeSettings((cur) => ({ ...cur, edgeWidth: v }))}
 							/>
 							<SettingSlider
 								label="Arrowhead size"
-								min={2}
+								min={1}
 								max={15}
-								step={1}
+								step={0.5}
 								value={settings.arrowLength}
 								onChange={(v) => changeSettings((cur) => ({ ...cur, arrowLength: v }))}
 							/>
 							<SettingSlider
 								label="Label size"
-								min={6}
+								min={3}
 								max={24}
-								step={1}
+								step={0.5}
 								value={settings.labelSize}
 								onChange={(v) => changeSettings((cur) => ({ ...cur, labelSize: v }))}
 							/>