build : fix xcframework + cmake clean-up (#27304)

* xcframework : fix build

* mtmd : remove unused include path

* vendor : use vendor::hash alias target in cmake

CMake reserves "::" in target names for imported/alias targets, so the real
target keeps the name vendor-hash and a vendor::hash ALIAS target is added.
Consumers (mtmd, llama-gguf-hash) now link against the namespaced alias.

Assisted-by: pi:llama.cpp/Qwen3.8-27B

* vendor : add cmake targets for all vendored libs with vendor:: aliases

Add INTERFACE targets for the header-only vendor libs (miniaudio, nlohmann,
sheredom, stb) and ALIAS targets named vendor::<lib> for all of them,
including cpp-httplib and hash. Each exposes the vendor/ root so includes
are namespaced, e.g. <nlohmann/json.hpp>.

Consolidate the per-lib add_subdirectory calls into a single
add_subdirectory(vendor), keeping the cpp-httplib gate on LLAMA_BUILD_COMMON.
Consumers (llama-common, mtmd) now link the aliases instead of relying on
raw vendor/ include paths.

hash: consumers now include via "hash/hash.h"; the vendor/hash dir is kept
as a PRIVATE include so the synced upstream sources compile unmodified.

Assisted-by: pi:llama.cpp/Qwen3.8-27B

* readme : use foo/bar names in acknowledgements

Assisted-by: pi:llama.cpp/Qwen3.8-27B

* ocd : fix valign

vendor/cpp-httplib/CMakeLists.txt

@@ -9,6 +9,8 @@ set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 
 add_library(${TARGET} STATIC httplib.cpp httplib.h)
 
+add_library(vendor::cpp-httplib ALIAS ${TARGET})
+
 # disable warnings in 3rd party code
 if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
     target_compile_options(${TARGET} PRIVATE /w)