CI: also build on push to main (code changes), keep cron for new releases

- push to main triggers a rebuild of the current version so build changes get
  tested; scoped to main so the job's pages/tag pushes can't loop it, and
  docs-only paths are ignored to avoid wasteful full rebuilds.
- the decide step treats a push (like a manual force) as build=true even when
  the version tag already exists.
- cron still handles new upstream binary releases as before.

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

README.md

@@ -85,9 +85,16 @@ The workflow targets a **self-hosted `act_runner`**. Because O3DE is large:
   access and add it as a secret named **`PUBLISH_TOKEN`** — the workflow prefers
   it automatically.
 
-Trigger it manually from the Gitea Actions UI (`workflow_dispatch`, with an
-optional **force** rebuild), or let the daily `cron` run it. It only rebuilds when
-the upstream version has no matching `vX.Y.Z` tag yet, so reruns are cheap no-ops.
+It runs on three triggers:
+
+- **`push` to `main`** — rebuilds whenever the build itself changes (always builds,
+  even for an already-published version, so you can test your change). Docs-only
+  changes (`README.md`, `docs/**`, `LICENSE*`, `.gitignore`) are ignored. Scoped to
+  `main` so the `pages`/tag pushes the job makes don't re-trigger it.
+- **daily `cron`** — picks up a **new O3DE binary release**; only builds when the
+  upstream version has no matching `vX.Y.Z` tag yet, so most days are cheap no-ops.
+- **`workflow_dispatch`** — manual run from the Gitea Actions UI, with an optional
+  **force** rebuild.
 
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