ci: run Build workflow on pushes to master

[Naturalclar]

Overview

The Build workflow's push trigger listed main, but this repository's default branch is master. The branch name never matched, so the push trigger has never fired and nothing validates the default branch after a merge.

 on:
   push:
     branches:
-      - main
+      - master

This is observable in the run history: every recent run of ci.yml was pull_request-triggered. The most recent runs attributed to master are from 2025 and predate the current configuration. In practice the repo has been relying entirely on pre-merge PR runs, with no post-merge signal on the default branch — so a merge that interacts badly with something else already on master would go unnoticed until the next PR happened to surface it.

This also matters for #1223 (automating npm publishing). Any release automation gated on CI wants a trustworthy green signal on the branch it publishes from; right now that signal does not exist.

Test Plan

The change is one word in a workflow trigger and cannot be exercised before merge — push triggers are read from the version of the workflow on the branch being pushed to, so the fix only takes effect once it is on master.

Verification performed:

• Confirmed the default branch is master via git remote show origin (HEAD branch: master). Creating a PR against main fails with a 422 base invalid, which is what surfaced this.
• Reviewed the ci.yml run history and confirmed every recent run carries the pull_request event, with no push runs since the trigger was configured.
• The jobs themselves are untouched, so lint, tsc, android, and ios (NewArch/OldArch) behave exactly as before. This PR's own checks run via the pull_request trigger and exercise the unchanged job definitions.

After merge, the next push to master should produce a Build run with event push — that run is the real confirmation.

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Generated by Claude Code