🔧 chore(standards): sync cpp playbook rules

Vendor standards live under docs/standards/playbook and are synced into .agents/cpp.

Add AGENTS.md entries so agents working in lsp-server follow the C++ ruleset and standards.

lsp-server/AGENTS.md

@@ -0,0 +1,23 @@
+# AGENTS (lsp-server)
+
+## Scope
+
+This directory tree (`lsp-server/`) contains the C++ codebase for the LSP server.
+
+## Rules
+
+- Follow the repository C++ agent ruleset: `.agents/cpp/index.md`.
+- Follow the vendored C++ standards snapshot:
+  - `docs/standards/playbook/docs/cpp/code_style.md`
+  - `docs/standards/playbook/docs/cpp/naming.md`
+  - `docs/standards/playbook/docs/cpp/toolchain.md`
+
+## Local tooling config
+
+This project already provides local configs:
+
+- `lsp-server/.clang-format`
+- `lsp-server/.clangd`
+- `lsp-server/CMakeLists.txt`
+- `lsp-server/CMakeUserPresets.json`
+- `lsp-server/conanfile.txt`