[zoedsoupe]

Problem

Dependencies and local setup versions were outdated, and the CI matrix only covered Elixir 1.18 with OTP 26/27. This mirrors supabase-ex#90.

Solution

• Update mix.lock to latest allowed versions via mix deps.update --all
• Expand the CI matrix (lint, static-analysis, test) to Elixir 1.20.2, 1.19.5 and 1.18.4 across OTP 25-28
• Bump the local dev shell to Elixir 1.20.2 on OTP 28 and nixpkgs to nixos-26.05-small
• Add a Compatibility section to the README stating support for the latest 3 stable Elixir versions

Rationale

mix.exs already required Elixir ~> 1.18, so the supported range is the latest 3 stable versions (1.20..1.18). The CI matrix and dev setup are aligned with that range, matching what was done in supabase-ex.