refactor: prefix private data members with m_

Rename all trailing-underscore private data members to the m_ prefix
required by AGENTS.md, across the auth, crypto, gip, mt76, and usb
transport classes plus the app session classes. Pure rename; no
behavior change. Full build and test suite pass.

Co-Authored-By: qwen3.8-27b@q3_k_xl: renamed members to m_ prefix

include/auth/crypto.hpp

@@ -48,7 +48,7 @@ public:
     auto finalize(std::array<u8, k_sha256_len>& out) -> void;
 
 private:
-    CC_SHA256_CTX ctx_;
+    CC_SHA256_CTX m_ctx;
 };
 
 // --------------------------------------------------------------------------
@@ -62,8 +62,8 @@ public:
     auto finalize(std::array<u8, k_sha256_len>& out) -> void;
 
 private:
-    sha256 inner_;
-    sha256 outer_;
+    sha256 m_inner;
+    sha256 m_outer;
 };
 
 // --------------------------------------------------------------------------