fix(build): stage Whisper runtime in macOS CI jobs

[meiiie]

Description
This is a focused fix for the macOS packaging path behind auto-captions. The GitHub macOS build and release jobs were still calling npm run build:native-helpers, which skips the bundled Whisper runtime. This switches those jobs to npm run build:platform-native-helpers so packaged macOS artifacts stage whisper-cli before Electron Builder runs.

Motivation
Issue #220 reports auto-captions failing immediately after pressing Generate. On current main, source builds already run build:platform-native-helpers, but the macOS CI packaging jobs did not, so packaged macOS builds could ship without the Whisper runtime and fail before transcription starts. I kept this scoped to the macOS packaging path only; the Windows reports in #220 may still need separate investigation.

Type of Change

• Bug Fix

Related Issue(s)
Related: #220

Screenshots / Video
Not included. This is a workflow-only change.

Testing Guide

• Reviewed the current caption generation path in electron/ipc/captions/generate.ts and the packaging workflows on main
• Confirmed the bundled Whisper runtime is built by npm run build:platform-native-helpers
• Confirmed the macOS jobs in .github/workflows/build.yml and .github/workflows/release.yml were still using npm run build:native-helpers
• Updated those macOS jobs to npm run build:platform-native-helpers
• Ran git diff --check
• Verified via grep that every macOS workflow path now uses build:platform-native-helpers

Checklist

• I kept the scope narrow
• I verified the changed workflow paths locally
• I did not run a real macOS build locally from this Windows host

[meiiie]

Manual build validation passed on this branch via Actions run 24902953791: build-macos, build-windows, and build-linux all completed successfully. That gives this workflow-only fix enough evidence for review, so I moved it out of draft. I am still keeping the scope narrow to the macOS packaging path behind #220 rather than claiming the Windows reports are fixed too.