ci: gate macOS build outside pull requests

[saagpatel]

What

• Add manual dispatch for the main CI workflow.
• Skip the full macOS build job during pull_request runs.

Why

• GitHub usage data showed AssistSupport has expensive macOS build minutes on PRs.

How

• Keep the existing Linux and macOS test jobs for PR validation.
• Run the full macOS build on push or manual dispatch instead of every PR.

Testing

• Parsed changed workflow YAML successfully.
• Not run: full product test suite, because this PR only changes workflow trigger behavior.

Performance Impact

• Expected to reduce macOS Actions minutes on pull requests.

Risk / Notes

• Full macOS build still runs outside PR events and can be manually dispatched.
• Existing concurrency cancellation remains in place.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Keep the required macOS build from passing when skipped

For pull_request runs targeting master, this skips the Build (macOS) job even though the repo's branch-protection notes list Build (macOS) as a required check (docs/plans/current-remediation-plan.md). GitHub documents that a job skipped by a conditional reports Success, so PRs can satisfy branch protection without ever running pnpm tauri build; a PR that breaks the packaged macOS app would only be caught after merge on the push workflow.

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