Document exported Catalyst APIs

[ChrisRackauckas-Claude]

This draft PR should be ignored until reviewed by @ChrisRackauckas.

Summary

• Add source-site docstrings for Catalyst-owned exported/public APIs that were missing them.
• Add missing Catalyst API entries to rendered docs pages.
• Add a non-canonical re-export API page so upstream re-exported names are rendered from their defining modules.

Verification

• timeout 3600 ~/.juliaup/bin/julia +1.10 --project=. -e 'using Catalyst; ...' reported EXPORTED_AND_PUBLIC_DOCSTRING_MISSING_COUNT 0.
• timeout 3600 ~/.juliaup/bin/julia +1.10 --project=. -e 'using Catalyst; ...' reported EXPORTED_AND_PUBLIC_RENDERED_DOCS_MISSING_COUNT 0.
• git diff --check passed.
• timeout 3600 ~/.juliaup/bin/julia +1.10 --project=. -e 'using Runic; exit(Runic.main(ARGS))' -- --check ... exits 1 with no diagnostics on touched files; --diff shows broad pre-existing Runic churn in these files, so I did not apply unrelated formatting.
• timeout 3600 env GROUP=Modeling ~/.juliaup/bin/julia +1.10 --project=. -e 'using Pkg; Pkg.test()' fails on this branch in DSL Options with 308 passed, 9 failed, 1 broken. The same failures reproduce on a clean origin/master worktree after temporarily converting the stale unexpected-pass @test_broken blocker at test/reactionsystem_core/reactionsystem.jl:1150 to @test so the suite can reach DSL Options.
• timeout 3600 ~/.juliaup/bin/julia +1.12 --project=docs docs/make.jl does not complete: after the API docs fixes it progresses to pre-existing inverse-problems example failures, starting with docs/src/inverse_problems/behaviour_optimisation.md:76-80 because OrdinaryDiffEq v7 no longer accepts verbose::Bool, followed by undefined variables from that failed block.