[php]: Fix documentation model header

[coffeemakr]

Fix the MD model header

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php members: @jebentier @dkarlovi @mandrean @jfastnacht @ybelenko @renepardon

---

Summary by cubic

Fixes duplicate H1 headers in generated PHP model docs. Model pages now use a single "# {Classname}" header for correct Markdown rendering.

• Bug Fixes
  • Removed the extra leading "#" in model_doc.mustache for php and php-nextgen to prevent "# # {Classname}" headers.
  • Regenerated PHP sample docs to reflect the corrected headers.

^{Written for commit a6475e8. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 185 files

Note: This PR contains a large number of files. cubic only reviews up to 75 files per PR, so some files may not have been reviewed.