docs(background): reduce default background job interval from 15min to 5min

feat(antigravity): ✨ add quota tracking with independent background jobs

refactor(auth): 🔨 relocate attribute declarations in BackgroundRefresher

feat(providers): ✨ implement credential tier initialization and persistence system

fix(auth): 🔨 tighten oauth refresh intervals, expand refresh buffers, improve logging and add iFlow docs

feat(auth): implement robust OAuth credential initialization and management

feat(provider): introduce OAuth credential management and custom provider handling