Feat/core offline hardening - #41

Summary

This PR delivers core offline hardening across storage, scheduler, voice AI, and cloud synchronization layers. It addresses concurrency locks, connection leakages, watchdog timeouts, and cloud pull foreign-key constraints, while expanding the automated test suite to 805 passing tests.

Key Changes

1. Local Storage & SQLite Resilience (src/storage/)

• Connection & Timeout Handling: Added resilient busy-handler retries and timeout protection to prevent SQLite database locks under high concurrent read/write loads.
• Session & Note Stores: Hardened user session handling, note tags/image URI persistence, and cleanup logic against null/undefined edge cases.
• Calendar & RRULE Helpers: Added validation guards for RFC 5545 ICS parsing and recurring event calculations to ensure corrupt calendar data degrades gracefully without crashing.

2. Scheduler & Proactive Reminders (src/scheduler/)

• Call Dispatcher Hardening: Resolved race conditions during background call dispatches; added fallback state machines when alarms trigger while the device is sleeping or transitioning between states.
• Recovery Daemon: Added automatic recovery for missed reminders after device reboots or app restarts.

3. Offline AI Pipeline & Watchdogs (src/ai/)

• Audio & Pipeline Watchdogs: Introduced timeouts on speech capture and Whisper/Kokoro inference bridges so the voice reminder flow never hangs indefinitely if native audio drops.
• TTS Cache Hygiene: Implemented cache sweeping to periodically purge stale generated voice audio files, preserving student device storage.
• NLU Parser Guards: Hardened JSON parser for SmolLM2 model outputs to validate expected schema fields and gracefully reject malformed payloads.

4. Cloud Sync & Data Integrity (src/sync/)

• Pull Integrity & Foreign Key Resolution: Fixed a critical bug where cloud pull assigned incoming records to a placeholder 'cloud' user ID, triggering foreign key constraint failures. Now binds the authenticated active user token to incoming upserts.
• Last-Write-Wins (LWW): Enforced timestamp-based conflict resolution so offline edits sync smoothly without clobbering newer server state.

5. Android Build & Runtime

• Gradle Optimization: Configured Gradle JVM args (-Xmx4096m) and disabled legacy Jetifier to ensure clean AAR compilation on modern React Native 0.86.
• Native Verification: Successfully compiled and validated on Android emulator (assembleDebug & installDebug).

Verification & Test Suite

All three mandatory checks pass with zero errors:

• TypeScript (npx tsc --noEmit): Clean (0 errors)
• Jest Unit & Integration Tests (npm test): 97 passed suites, 805 / 805 passed tests (460 new tests added)
• ESLint (npx eslint src/): Clean (0 errors)