fix: align sidebar section and footer icon columns, bump v0.1.56

Section header and footer link icons were at different x-positions (9px
vs 15px) and used different wrapper widths (16px vs 18px), producing a
ragged left column where the two rows are visually adjacent.

- Drop horizontal padding from .bottom so .bottomItem sits flush to the
  sidebar edges like .treeSection, yielding a shared 9px effective left
  padding (3px transparent border + 6px inner).
- Rewrite .bottomIcon to mirror .sectionIcon: 16px flex-centered, no
  legacy font-size/text-align (obsolete for Lucide SVG icons).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@cameleer/design-system",
-  "version": "0.1.55",
+  "version": "0.1.56",
   "type": "module",
   "main": "./dist/index.es.js",
   "module": "./dist/index.es.js",