cmake : remove STATIC from impl libraries, enable LLAMA_BUILD_APP by default (#23462)

* cmake : remove STATIC from impl libraries, allow BUILD_SHARED_LIBS control

Remove explicit STATIC from all -impl libraries (server, cli, completion, bench,
batched-bench, fit-params, quantize, perplexity) so BUILD_SHARED_LIBS controls
shared vs static linkage.

Add WINDOWS_EXPORT_ALL_SYMBOLS ON for proper DLL export on Windows.

Assisted-by: llama.cpp:local pi

* cmake : enable LLAMA_BUILD_APP by default

Assisted-by: llama.cpp:local pi

* ci : disable app in build-cmake-pkg.yml