feat: add native SQLite storage and CLI capture

[shettyh]

Summary

• replace production IndexedDB persistence with a shared native Rust/SQLite collection used by both Tauri and the CLI
• add rem deck list and atomic rem card add workflows with JSON input/output, dry runs, duplicate handling, and stable exit codes
• protect Git sync from concurrent local writes with revision-checked merge retries while keeping the Git wire format unchanged
• package CLI archives for macOS, Linux, and Windows, update the installer/release workflows, and add CLI docs plus an agent capture skill
• update the README for SQLite storage, CLI installation/capture, agent usage, and workspace development checks

Design notes

• no IndexedDB-to-SQLite migration is included because the project currently has no users to migrate
• CLI capture is local-only and does not trigger Git sync; cards join Git on the desktop app's next sync
• Dexie remains only as a browser-test adapter

Verification

• npm test — 55 files / 332 tests
• npm run build
• npm audit --audit-level=high — 0 vulnerabilities
• cargo fmt --all --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace — 76 tests
• tools/test-install.sh
• npm run app:build and local macOS CLI archive smoke test

Linux and Windows release artifacts are configured for their GitHub Actions runners; local packaging was verified on macOS.