[nightly-review] Keep Apple summaries tied to transcript participants

[r3dbars]

Summary

• keep local summary participant metadata sourced from transcript speaker labels for every provider
• apply the same transcript-derived participant override to the Apple on-device summary path that Gemma already used
• add a fast regression covering provider output that omits participants

Nightly evidence

• recent health signal still shows meeting degradation/speaker-finalization events, but those are pre- or not-yet-shipped relative to yesterday's instrumentation patch
• the highest-confidence current-main bug found tonight was in the new local summary provider split: Apple summaries could write None found. participants even when the transcript had canonical speaker labels

Verification

• bash scripts/dev/agent-preflight.sh Sources/Meeting/LocalMeetingSummarizer.swift Tests/LocalMeetingSummarizerTests.swift
• bash build-deps.sh --force
• bash build.sh --no-open
• bash run-tests.sh (4,656 passed)
• bash run-integration-smoke.sh
• /Users/redbars/.codex/skills/codex-review/scripts/codex-review --mode local --output /tmp/transcripted-nightly-codex-review-20260611.txt (clean)