Improve RTSP server input validation and build configuration

[ptamb3]

Motivation

• Harden startup behavior by validating the provided media path and avoiding embedding unescaped paths into the GStreamer pipeline.
• Fix CMake metadata and linking variables to match expected project layout and GStreamer pkg-config variables.
• Clarify README instructions to avoid confusion about the Makefile location and correct minor wording.

Description

• Added #include <string.h> and an early check using g_file_test(argv[1], G_FILE_TEST_EXISTS | G_FILE_TEST_IS_REGULAR) to fail fast when the media path is missing or not a regular file in src/rtsp_server.c.
• Escaped and quoted the media path with g_strescape and injected the escaped value into the GStreamer launch string, and freed the escaped string afterwards in src/rtsp_server.c.
• Renamed the CMake project to rtsp_server and corrected link_directories to use GSTREAMER_LIBRARY_DIRS in CMakeLists.txt.
• Fixed README wording and clarified that the Makefile build flow lives in src/ in README.md.

Testing

• Attempted to configure and build with cmake -S . -B build && cmake --build build, which failed in this environment because the glib-2.0/gobject-2.0 development packages are not installed (failure is environmental, not due to the changes).
• No unit tests are present in the repository and no additional automated tests were executed.

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[chatgpt-codex-connector]

Require regular file when validating input path

g_file_test() treats combined GFileTest flags as an OR, so G_FILE_TEST_EXISTS | G_FILE_TEST_IS_REGULAR succeeds for any existing path, including directories. In this case a directory argument bypasses the new guard and the server continues until GStreamer fails at runtime when filesrc tries to open it as a file, which defeats the intended fail-fast validation. Use G_FILE_TEST_IS_REGULAR alone (or separate checks) to enforce a real file.

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