refactor: rename Organisation → Company, Membership → CompanyMembership

fix(ci): use mix do for single VM — compile + ecto + test together

fix(ci): debug beam file listing after compile

fix(ci): add Code.ensure_loaded! debug + single run block

fix(ci): explicit MIX_ENV=test on each command + debug build dir

fix(ci): single run block, no deps.compile (compile handles deps)

fix(ci): use 'mix do' to keep single BEAM VM across steps

fix(ci): use Elixir 1.18.3 / OTP 27.3 — stable for CI

fix(ci): add debug output to find missing BEAM files

fix(ci): single step with explicit hex/rebar setup, no caching

fix(ci): only cache deps, not _build — prevents stale BEAM files

fix(ci): force clean build to clear stale OTP 28 BEAM files

fix(ci): combine compile + test into single step

fix(ci): include OTP/Elixir version in cache key

fix(ci): downgrade to Elixir 1.17.3 / OTP 27.2