webget 0.8.0 - MCP authenticated sessions

Added

• MCP server: list_profiles tool (non-sensitive session metadata) and profile parameter on fetch / search_fetch for authenticated scraping with locally stored sessions (webget login). Cookie values are never exposed; invalid or unknown profile names return clean errors instead of a silent anonymous fallback.
• WEBGET_PROFILE_DIR env override for the profile root (tests/ops).

Backward compatible: profile omitted behaves exactly like 0.7.3. Full suite + browser integration + MCP E2E (cookie-gated auth) verified.