cli: add oak-cli, the first pure C ABI consumer of liboakengine

- oak-cli info prints project/sequence/footage details; oak-cli render
  writes PPM frames and a PCM WAV through the facade only - no engine
  C++ headers, no Qt headers, links just liboakengine
- exit code 2 marks rendering-unavailable so ctest can skip cleanly on
  machines without a GL render backend; info test runs everywhere
- facade fix uncovered by the CLI: project load now absolutizes the
  path, so relative footage paths can't be mistaken for a moved
  project; the fixture project now carries probed footage wired into
  its sequence so it renders real content
- packaged like the other binaries (Linux bin install, macOS bundle,
  Windows DLL copies); DESTDIR-verified

CMakeLists.txt

@@ -309,6 +309,7 @@ add_subdirectory(third_party/KDDockWidgets EXCLUDE_FROM_ALL)
 
 add_subdirectory(third_party/openfx/HostSupport)
 add_subdirectory(engine)
+add_subdirectory(cli)
 
 # Everything above the engine library links against it
 list(APPEND OLIVE_LIBRARIES oakengine)