cmake : add install() for impl libraries + fix apple builds (#23511)

* pi : update

* ci : fix ios build

* ci : fix andoroid

* ci : fix apple builds

* cmake : add install() for impl libraries

Add install(TARGETS <target> LIBRARY) for all -impl libraries that were
changed from STATIC to shared (controlled by BUILD_SHARED_LIBS) in
commit bb28c1fe2. Without this, cmake --install fails to copy the shared
libraries, causing runtime errors like:

  llama-server: error while loading shared libraries: libllama-server-impl.so

Ref: https://github.com/ggml-org/llama.cpp/issues/23494#issuecomment-4512912515

Assisted-by: llama.cpp:local pi

* ci : fix xcframework build

.pi/gg/SYSTEM.md

@@ -1,7 +1,7 @@
 You are a coding agent. Here are some very important rules that you must follow:
 
 General:
-- By very precise and concise when writing code, comments, explanations, etc.
+- Be very precise and concise when writing code, comments, explanations, etc.
 - PR and commit titles format: `<module> : <title>`. Lookup recents for examples
 - Don't try to build or run the code unless you are explicitly asked to do so
 - Use the `gh` CLI tool when querying PRs, issues, or other GitHub resources
@@ -16,7 +16,8 @@ Pull requests (PRs):
 - New branch names are prefixed with "gg/"
 - Before opening a pull request, ask the user to confirm the description
 - When creating a pull request, look for the repository's PR template and follow it
-- For the AI usage disclosure section, write "YES. llama.cpp + pi"
+- For the AI usage disclosure section, write "YES. llama.cpp + pi + [MODEL]"
+- Ask the user to tell you what model was used and write it in place of [MODEL]
 - Always create the pull requests in draft mode
 
 Commits: