Align docs with StyleGuide and add CLAUDE.md

- Rename 16 kebab-case docs to PascalCase per StyleGuide
- Move per-language client design docs from docs/ to clients/<lang>/
  alongside their READMEs
- Add ## Related Documentation sections to 15 docs that lacked one
- Fix sentence-case violations in H3 headings (StyleGuide rule)
- Update cross-references in gateway.md, client READMEs, scripts,
  and generate-proto.ps1 helpers to follow the new paths
- Add CLAUDE.md with build/test commands, the source-update
  verification matrix, the parity-first contract, and pointers
  to MXAccess and Galaxy Repository analysis sources

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/python/generate-proto.ps1

@@ -7,7 +7,7 @@ $outputRoot = Join-Path $PSScriptRoot 'src\mxgateway\generated'
 $python = 'C:\Users\dohertj2\AppData\Local\Programs\Python\Python312\python.exe'
 
 if (-not (Test-Path $python)) {
-    throw "Python was not found at $python. See docs/toolchain-links.md."
+    throw "Python was not found at $python. See docs/ToolchainLinks.md."
 }
 
 New-Item -ItemType Directory -Path $outputRoot -Force | Out-Null