Cuts v0.6.0 collecting the work merged since 0.5.0 — session
persistence (#35), native MCP support (#36), first-class LSP
integration (#37), and the consecutive-mistakes counter fix (#38) —
plus two test-stability fixes uncovered while preparing the release:

- test/ex_athena/sessions/stores/ets_test.exs — wrap GenServer.stop
  in setup/on_exit so cleanup tolerates a Jsonl process that died
  between whereis and stop. Race showed up under certain seeds.

- test/ex_athena/lsp/implicit_diagnostics_test.exs — on_exit now
  resets :lsp_implicit_diagnostics_enabled to false (matching
  config/test.exs) instead of Application.delete_env/2, which let
  the module's literal default of true leak into subsequent tests
  in the same file.

Also adds an MCP module group to mix.exs docs/groups_for_modules so
ExAthena.Mcp.* renders as its own section in HexDocs.