ci: auto-trigger dist build on push to main, use dist branch name

Push to `main` now auto-triggers the build-dist workflow. The `main`
branch pushes to `dist` (matching the `pds` convention) instead of
`main-dist`; other branches still get `<branch>-dist`.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: ryan-williams

.github/workflows/build-dist.yml

@@ -1,6 +1,8 @@
 name: Build dist branch
 
 on:
+  push:
+    branches: [main]
   workflow_dispatch:
     inputs:
       source_ref:
@@ -42,7 +44,12 @@ jobs:
           SHORT_SHA: ${{ steps.info.outputs.short_sha }}
           SOURCE_VERSION: ${{ steps.info.outputs.version }}
         run: |
-          DIST_BRANCH="${SOURCE_REF}-dist"
+          # `main` pushes to `dist` (matching pds convention); other branches get namespaced
+          if [ "$SOURCE_REF" = "main" ]; then
+            DIST_BRANCH="dist"
+          else
+            DIST_BRANCH="${SOURCE_REF}-dist"
+          fi
           DIST_VERSION="${SOURCE_VERSION}-dist.${SHORT_SHA}"
 
           # Configure git