Add Cursor provider adapter

## Goal Add Cursor as a Lineage provider target. ## Why Cursor is one of the most common AI-native coding environments. Lineage should be able to materialize package assets that Cursor can use without leaking Cursor-specific assumptions into core package semantics. ## Scope - Define the Cursor adapter boundary. - Decide whether Cursor support is command launch, config/materialization, or both. - Materialize supported package assets into Cursor-compatible locations. - Keep Cursor-specific file names and settings out of core runtime code. - Add dry-run/inspect output showing what Cursor support will do. ## Acceptance Criteria - Cursor support is behind an explicit provider adapter. - A package can expose Cursor-relevant skills, rules, MCP config, or references when supported. - Receiver-side writes are permission-gated or clearly shown before materialization. - Tests cover adapter discovery/materialization behavior. - Docs explain current Cursor support honestly.