v0.7.0 — per-session isolated contexts

Added

• browser_context (#39): open/switch/close/list named incognito-style contexts that share nothing with the persistent profile. All tools act on the active context; the stealth script and origin fence apply per context. Pair with browser_load_state to inject scoped auth into a clean context. In-memory only; lost on browser_close/browser_handoff.

Full details in CHANGELOG.md.