Fix build and run unit tests

[erizhang]

Resolves project build failures and enables unit tests.

The project encountered several build issues:

• A global function pointer shutdown_server was defined in a header, causing multiple definition errors. This is now declared extern in the header and defined in a source file.
• The main executable was linked using cc instead of g++, leading to linker errors with the CppUTest C++ library. The linker command now uses g++.
• Corrected typos in the Makefile (e.g., PRDUCT_MAIN_OBJ, localhst:8888).
• Removed the automatic execution of the main program from the Makefile to prevent build blockage.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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