fix(icons): serve icons no-cache so updates propagate (2.5.2)

Icon route used Cache-Control: public, max-age=86400, so changed icons stayed
stuck in CF + browser caches for a day. Switch to no-cache (revalidate; Express
ETag => 304 when unchanged) so icon edits show up immediately.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "void-server",
-  "version": "2.5.1",
+  "version": "2.5.2",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "void-server",
-      "version": "2.5.1",
+      "version": "2.5.2",
       "dependencies": {
         "@modelcontextprotocol/sdk": "^1.29.0",
         "@mozilla/readability": "^0.6.0",