Document umbrella re-exported API

[ChrisRackauckas-Claude]

Important

Please ignore this draft until it has been reviewed by @ChrisRackauckas.

Summary

• add a rendered Common Interface API page for all 33 non-algorithm exports of the OrdinaryDiffEq umbrella module
• register concise umbrella doc entries while retaining the owning SciMLBase documentation
• add the owner modules as direct documentation dependencies
• include the EnsembleContext documentation needed by EnsembleProblem cross-references

Clean-master root cause

The exact global QA lane fails on clean master because SciMLTesting 2.3 enables rendered public-API checks by default. The umbrella module exported 33 common interface names, but none appeared in an @docs or @autodocs block.

A first-parent boundary check found commit d7a66c0 passing 6/6 immediately before merge commit 12b6996, while 5766b7c fails 7 passed / 1 failed with all 33 names. The boundary commit raised the SciMLTesting compatibility from 1.7 to 2.1, allowing the newly released 2.3 behavior.

Validation

• Julia 1.12 exact QA replay: GROUP=QA, Pkg.test with allow_reresolve=true — 8/8 passed
• full Julia 1.12 documentation build — exited 0; the new page has no missing-doc, binding, cross-reference, or build errors
• whole-repository Runic check — exited 0
• git diff --check — exited 0
• docs Project.toml and Manifest.toml parse successfully

The rendered page is 102.32 KiB, slightly above Documenter's 100 KiB warning threshold and below its 200 KiB hard threshold. No warning was disabled or added to warnonly.