OSCAR Viewer 3.9.1: offline alarm QR transfer

[tyronechrisharris]

Why

Air-gapped sites need a compact way to move an alarm summary and its detector curves to an authorized second device without relying on network services.

What changes

• Export alarms from the dashboard preview or Event Details as a QR code, PNG, or portable .oscar-alarm.json file.
• Include source/event/adjudication metadata and adaptively downsampled gamma, neutron, and threshold series while preserving endpoints, extrema, and threshold crossings.
• Add an Alarm Transfer page for camera scan, saved-image scan, file or text import, integrity validation, chart reconstruction, download, and Web Share.
• Add complete English, Spanish, French, and Greek UI strings.
• Enforce strict import limits and clearly state that SHA-256 detects corruption but does not authenticate a sender; packages are not encrypted or signed.

Baseline

Built directly on the Viewer commit pinned by the OSCAR v3.9.0 release (4b49c7c). This PR targets 3.9.1.

Verification

• npm ci
• npm run validate:locales (401 complete keys in en/es/fr/el)
• npx tsc --noEmit --pretty false --traceResolution false
• npm run test:alarm-transfer (6 passing)
• npm run test:event-filter (6 passing)
• npm run build (production compile and MQTT bundle verification pass)