v0.7.0

• Opt-in per project (breaking default change). A globally-installed plugin no longer
  activates in every workspace. Presence of .engraim/ is the sole opt-in signal:
  • The SessionStart hook is fully silent in a project that hasn't opted in — it creates
    nothing and injects nothing (previously it auto-bootstrapped .engraim/ on first session).
  • The MCP server refuses to auto-create a workspace: every tool except the new opt-in
    tool no-ops with a pointer to /engraim:init until .engraim/ exists.
  • New enable tool + cli enable subcommand are the only paths that adopt a project;
    /engraim:init, /engraim:onboard, and /engraim:backfill call it first.
  • Existing opted-in workspaces are unaffected (they already have .engraim/).