Revert Documenter compat bump to keep docs build green

Documenter v1 makes \`missing_docs\` and \`unused_footnote\` fatal,
which surfaces pre-existing issues (12 undocumented exports across
src/gp.jl/strategies + ~20 stale footnotes in docs/src/{mutation,
selection,crossover}.md). On master these have been silent warnings
because docs/Project.toml pins Documenter to "0.26".

Reverting the compat bump restores the master behavior. The
documentation cleanup (adding missing API references and pruning
unused footnotes) belongs in a follow-up PR, not in CI-infra work.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>

Author: ChrisRackauckas

docs/Project.toml

@@ -3,4 +3,4 @@ Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
 Evolutionary = "86b6b26d-c046-49b6-aa0b-5f0f74682bd6"
 
 [compat]
-Documenter = "1"
+Documenter = "0.26"