Point branch references at main

Workflow triggers, package and gem metadata URLs, and install instructions
name the branch that CI runs on and that the repository serves by default.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HPCkcoEjWRnxMfS2yKUZFs

Author: RISCfuture

.github/workflows/ci.yml

@@ -2,9 +2,9 @@ name: CI
 
 on:
   push:
-    branches: [master]
+    branches: [main]
   pull_request:
-    branches: [master]
+    branches: [main]
 
 permissions:
   contents: read

.github/workflows/deploy.yml

@@ -7,7 +7,7 @@ on:
   # Runs when CI passes
   workflow_run:
     workflows: [CI]
-    branches: [master]
+    branches: [main]
     types: [completed]
 
 permissions: