chore: swap Discord for GitHub Discussions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/ISSUE_TEMPLATE/config.yml

@@ -1,8 +1,7 @@
 blank_issues_enabled: true
 contact_links:
-  - name: Discord
-    # TODO: replace with actual Discord invite link
-    url: https://discord.gg/YOUR_INVITE
+  - name: Discussions
+    url: https://github.com/zenchantlive/beadboard/discussions
     about: Chat with the community, coordinate on contributions, get help
   - name: Available work
     url: https://github.com/zenchantlive/beadboard/issues?q=is%3Aissue+is%3Aopen+label%3Acontrib%3Aopen