ci(mobile): collapse OTA matrix to single job with parallel code-push

[dylanjeffers]

Summary

Builds on #14326 (which already added node_modules cache reuse in the OTA job and decoupled OTA from mobile-verify) by further collapsing the iOS/Android OTA matrix into a single job.

• The previous matrix (platform: [ios, android]) parallelized publishing but at the cost of running the full setup pipeline — checkout, setup-node, patch checksum, cache restore, npm run postinstall/npm ci, AWS config — on two separate runners. That setup is the bulk of the wall time on each runner.
• This change runs both platforms on one runner and parallelizes only the code-push create-history/code-push release calls via background processes (ios & android & wait), which is the part that actually benefits from running concurrently. Per-platform stdout/stderr is captured to log files and emitted under ::group:: headers so each platform's output stays readable. Exit status from both platforms is aggregated so a failure on either still fails the job.
• Applied symmetrically to both mobile-ota-release (rc channel) and mobile-ota-release-production (production channel).

For reference, the three optimizations described in the brief map to:

1. Cache reuse in OTA — already in main (ci(mobile): cache deps + parallelize OTA + decouple lint to speed up OTA ~3x #14326); cache key npm-cache-mobile-${{ runner.os }}-node-${{ env.NODE_VERSION }}-${{ hashFiles('package-lock.json') }}-${{ steps.patch-file.outputs.patch_checksum }} matches the mobile-install writer, and the install step short-circuits to npm run postinstall on hit.
2. Parallel iOS + Android code-push — this PR (background processes within one job).
3. Decouple from verify/lint — already in main (ci(mobile): cache deps + parallelize OTA + decouple lint to speed up OTA ~3x #14326); OTA depends on [mobile-install, mobile-version-check], not mobile-verify.

Test plan

• Workflow YAML parses (validated locally with python3 -c "import yaml; yaml.safe_load(...)")
• Trigger an rc OTA release (push to main without a version bump, or workflow_dispatch with ota_channel=rc) and confirm both iOS and Android code-push release calls complete successfully and the published bundles are reachable
• Trigger a production OTA release via workflow_dispatch with ota_channel=production and confirm the environment approval gate still fires and both platforms publish
• Force-fail one platform (e.g. invalid OTA_APP_VERSION) and confirm the job still fails even though the other platform succeeded — both logs should appear in the job output

🤖 Generated with Claude Code

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