docs(fix): add cross-links between C++ and Python origin docs (#165)

- Fix 5 broken links to nonexistent docs (custom-origin-python.md,
  python-silo-origin.md, python-custom-origin-guide.md) by pointing
  to closest existing content
- Add Python cross-references (kcsdk-python.md, silo guide) to 7
  C++ origin doc See Also sections
- Add C++ foundation links (OriginManager, FileOrigin, FileOriginPython,
  CommandOrigin) to kcsdk-python.md and guide/silo.md
- 9 files updated, 16 cross-links added

docs/src/reference/cpp-file-origin.md

@@ -196,4 +196,7 @@ fallback** — it owns any document that no other origin claims.
 - [OriginSelectorWidget](./cpp-origin-selector-widget.md) — toolbar
   dropdown for switching origins
 - [Creating a Custom Origin (C++)](../guide/custom-origin-cpp.md)
-- [Creating a Custom Origin (Python)](../guide/custom-origin-python.md)
+- [KCSDK Python API](./kcsdk-python.md) — Python bindings for origin
+  registration and document-origin resolution
+- [Silo Guide — Origin Integration](../guide/silo.md#origin-integration) —
+  `SiloOrigin` as a real-world `FileOrigin` implementation in Python