Generate Markdown documentation with ExDoc 0.40.3

[BobbieBarker]

Summary

• require ExDoc 0.40.3 or newer for documentation builds
• add ExDoc's Markdown formatter alongside the existing HTML formatter
• refresh the locked documentation-only dependencies

Why

ExDoc 0.40 introduced native Markdown output and an llms.txt index. Publishing those artifacts on HexDocs gives documentation retrieval tools, MCP documentation servers, and coding agents a canonical machine-readable source instead of requiring them to scrape rendered HTML. Broader adoption makes Elixir library documentation easier to discover and use across the ecosystem.

This keeps ConCache's existing HTML documentation intact while adding the Markdown pages and index. Once this is merged, please publish or republish the documentation at your earliest convenience so these artifacts become available on HexDocs and the community can benefit from them.

Compatibility

ExDoc remains a development-only dependency with runtime: false, so this does not change ConCache's ~> 1.7 Elixir requirement, runtime dependency graph, or public API. Generated documentation is not committed.

Verification

• unmodified baseline: MIX_ENV=dev mix docs produced HTML, with no llms.txt or Markdown pages
• changed build: MIX_ENV=dev mix docs produced HTML, llms.txt, and 5 Markdown pages
• verified every Markdown link listed in llms.txt resolves to a generated file (4/4)
• mix format --check-formatted
• mix deps.unlock --check-unused
• mix dialyzer — 0 errors
• MIX_ENV=test mix compile --warnings-as-errors
• mix test — 68 tests, 0 failures

The project checks above were run with Elixir 1.16.2, matching the repository's configured Elixir version.