Add a panZoomGestures action: one-finger/left-button drag pans, two-finger
pinch and Ctrl+wheel zoom around the centroid, plain wheel pans. Pan is
edge-clamped via clampPan (no infinite scroll), a real drag suppresses the
trailing node click, and inertia decays after release unless prefers-reduced-
motion. Canvas container switches from native scroll to overflow-hidden.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Degrade Infinity/NaN/overflow per axis and clamp zoom into bounds so a crafted
?cx/?cy/?z shared link cannot blank the SVG (Nora's review).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
