Refactor SyncResolver to unified state machine with single-pass connection flow

[guiyanakuang]

Problem

The current SyncResolver has several design issues that make device connections slower and the code harder to maintain:

1. Two-phase connection with event round-trip: Connecting from DISCONNECTED requires two separate event cycles (ResolveDisconnected → CONNECTING → ResolveConnecting → CONNECTED), adding unnecessary latency.

2. Implicit UNVERIFIED state: UNVERIFIED is a side-effect of tokenCache miss during resolveConnecting, not an explicit state transition.

3. Complex state transition paths: State transitions are scattered across resolveDisconnected, resolveConnecting, resolveConnection, and tryUseTokenCache with implicit dispatch logic.

4. Redundant event types: Four separate resolve events (ResolveDisconnected, ResolveConnecting, ResolveConnection, ForceResolveConnection) where two suffice.

Solution

Refactor the internal state machine while keeping the external protocol unchanged (VERSION=3, all HTTP endpoints, DB schema — fully compatible with old devices):

• Unify 4 resolve events into 2: Resolve and ForceResolve
• Replace scattered resolve methods with a clear phase-based flow: resolve → discoverAndConnect → authenticate → tryTokenCacheOrUnverified / verifyConnection
• Complete the full discover → authenticate flow in a single resolve pass (no intermediate event round-trip)
• Avoid unnecessary DB writes when state doesn't change (e.g., UNVERIFIED polling)