Salvage useful PR 1352 deltas

[r3dbars]

Summary

• Salvages the still-useful App-improvement follow-through: action-item done/due metadata, semantic search, silent-failure instrumentation, disk guards #1352 action item metadata slice: quick summaries can emit due hints, CaptureKit parses due/status markers, and MCP list/digest/recap keeps that metadata.
• Raises the pre-recording free-space guard from 100MB to 1GB.
• Adds one-shot Parakeet pending-buffer truncation telemetry when old samples are dropped.

Live comparison / scope killed

• App-improvement follow-through: action-item done/due metadata, semantic search, silent-failure instrumentation, disk guards #1352 is closed and unmerged; this branch was rebuilt from current main instead of reviving it.
• Rebuild MCP search and receipt tools #1375 already replaced the semantic/hybrid search, receipt/recent_context, and recap-preview parts. Keep those out of this PR.
• Report audio maintenance telemetry #1384 already replaced retained-audio maintenance telemetry and capture-library-size reporting. Keep those out of this PR.
• Leave the old route-recovery churn dead unless a fresh current-main repro proves it is still needed.

Verification

• codex review --base origin/main clean after fixes. Earlier review found MCP due/status search + recap output gaps and stale schema copy; both were fixed.
• bash build-deps.sh --force
• bash build.sh --no-open
• bash run-tests.sh (12331 passed)
• bash run-integration-smoke.sh
• bash run-e2e-smoke.sh
• swift test (608 tests, 2 skipped)
• swift test --package-path Tools/TranscriptedCaptureKit (48 tests)
• swift test --package-path Tools/TranscriptedCLI (78 tests)
• swift test --package-path Tools/TranscriptedMCP (158 tests)
• git diff --check

lanes used: Codex=live GitHub compare, rebuild, tests, independent review, PR; Claude=skipped; Local=skipped; Windows=skipped