feat(handles): allow 1-48 bottom connection points via slider

Replaces the 4-option dropdown with a 1..48 slider. Existing handle IDs
('bottom', 'bottom-2'..'bottom-4') are preserved and the hand-tuned pixel
positions for counts 1..4 are locked in (regression-tested) so saved
canvases render identically. Counts >=5 use uniform spacing; node card
auto-grows in width so handles stay clickable. Existing edge-remap on
shrink scales unchanged thanks to its index-based loop.

ha-relevant: yes

frontend/src/types/index.ts

@@ -93,6 +93,7 @@ export interface NodeData extends Record<string, unknown> {
     height?: number
   }
   custom_icon?: string
+  /** Number of bottom connection points, 1..48. Default 1 (centered). */
   bottom_handles?: number
 }