Fix: RAD web connection stability and mobile UI overflow

[SeleiXi]

Summary

This PR improves RAD web client stability, model discovery, and mobile usability.

Changes

• Stabilize bridge connection lifecycle and prevent duplicated or stale connection state.
• Merge live bridge output into thread reads so active sessions stay consistent.
• Add retry behavior for default pairing on startup.
• Tolerate relay heartbeat jitter in the bridge to reduce unstable disconnects.
• Fix static asset stream error handling.
• Repair shortened device ID label rendering.
• Fix mobile chat and sidebar overflow issues, including long thread names forcing horizontal scrolling.
• Add support for flexible model IDs and paginated runtime model fetching, including cursor edge cases.
• Simplify the disconnected/local bridge flow so users do not need to manually paste JSON as the primary path.
• Add focused web-client unit tests for server behavior and model list pagination.