[lonlydwolf]

The XOR parent still pinned the pre-closeout C++ and C# implementations and described defects that their reviewed PRs have now fixed. This updates the aggregate project to include both completed repairs.

• Pin C++ to merged commit 330b73b04f1a86ed35d61e9bf2e944a680e7c484 and C# to 85f608eaf7cfc9eb6234f29b8d9337a271f3db97. The Python pin is unchanged.
• Add root-relative build/run/test instructions for all three languages and replace stale missing-data/error-state warnings with current scope and limitations.
• Extend parent CI to check the pinned C++ code on Linux/macOS and C# on Linux, alongside existing Python Linux/Windows checks.
• Document differences in initialization, momentum and training budgets without claiming cross-language numerical parity.

Validation: cloned this branch recursively into a fresh directory and ran the documented examples and suites from the parent root. All three demos classified 4/4 XOR inputs; Python's three tests, C++ regression/convergence checks and C#'s four regression groups passed. C++ compiled with warnings enabled; C# Release build had zero warnings/errors. Independent review found no blockers.

The companion PRs are merged and their repositories archived:

• Make the C++ XOR exercise reproducible before archival Cpp-Neural-Network#1
• Make the C# XOR exercise runnable before archival C-Sharp-Neural-Network#1

The parent was temporarily unarchived to open this PR. After review and merge, rearchive it as a completed learning exercise. This PR changes parent documentation/CI and gitlinks only; it adds no language implementation changes.