feat: add opt-in smart auto-refresh with per-provider settings

[victorhqc]

Summary

Adds per-provider automatic refresh controls and shared Regular and Smart settings. Smart mode uses recent usage changes to choose a faster or slower refresh interval.

Why

Users need control over periodic provider checks and their potential quota use. This implements the approved refresh behaviour in (core 08).

What changed

• Added persistent per-provider opt-in settings, with automatic refresh off by default.
• Added Smart refresh policy and completion-based scheduling that prevents overlapping work.
• Added localized, accessible Refresh Settings controls.
• Added provider metadata for automatic-refresh disclosures and a Claude Code quota warning.
• Updated Claude Code refresh caching for the shortest Smart interval.
• Added coverage for preferences, policy decisions, scheduling, and provider metadata.

Notes for review

• Review the refresh lifecycle around settings changes, provider disablement, and failed proactive checks.
• Automatic refresh remains inactive until a user enables it for a provider.