v2.3.2: fix truncated download cache, update Discord link

Fix pre-release downloads failing with "unexpected EOF" by validating
cached PWR file sizes against manifest expected sizes. Previously only
checked > 1MB which accepted truncated files. Also update Discord
invite link to new server across all files.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main.js

@@ -89,7 +89,7 @@ function setDiscordActivity() {
         },
         {
           label: 'Discord',
-          url: 'https://discord.gg/hf2pdc'
+          url: 'https://discord.gg/Fhbb9Yk5WW'
         }
       ]
     });