Desktop client: offline cache + WebSocket approval handler

[ahmetabdullahgultekin]

Why: Desktop has no push (no APNs/FCM) and no graceful offline behavior.

Done when:

• Offline cache: Compose UI degrades gracefully and shows last-known profile + session info from an encrypted cache (Desktop gap docs: add comprehensive ADD critique report with gap analysis #7, ~1 d).
• WebSocket approval handler: fallback for push via wss://api.fivucsas.com/ws/approvals (Desktop gap docs(website): add FIVUCSAS landing website ADD #8, ~3 d).

source: plans/CLIENT_APPS_PARITY.md:140

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Migrated from plans/CLIENT_APPS_PARITY.md (git history retains the original).