Add Android arm64 CPU profile selection and variant loading

[leehack]

Summary

• Add Android arm64 CPU variant policy support to hook config with cpu_profile (full default, compact) and advanced cpu_variants override.
• Update backend module loading to support dotted CPU variant names (for example libggml-cpu-android_armv8.2_2.so) and avoid CPU preload pinning when using load-all auto-selection.
• Bump native bundle tag in hook to b8157 and document new Android CPU policy options in installation/support docs.

Validation

• dart analyze hook/build.dart lib/src/hook/native_bundle_config.dart lib/src/backends/llama_cpp/llama_cpp_service.dart test/unit/hook/native_bundle_config_test.dart
• dart test test/unit/hook/native_bundle_config_test.dart
• dart test test/unit/backends/llama_cpp/llama_cpp_service_test.dart
• dart test test/unit/hook/build_hook_integration_test.dart test/unit/hook/build_hook_linux_integration_test.dart

[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.66667% with 47 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.48%. Comparing base (b39e062) to head (2611c51).
⚠️ Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/src/backends/llama_cpp/llama_cpp_service.dart	24.48%	37 Missing ⚠️
lib/src/hook/native_bundle_config.dart	89.13%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #72      +/-   ##
==========================================
- Coverage   76.54%   76.48%   -0.07%     
==========================================
  Files          66       66              
  Lines        8216     8338     +122     
==========================================
+ Hits         6289     6377      +88     
- Misses       1927     1961      +34     

Flag	Coverage Δ
unittests	76.48% <66.66%> (-0.07%)	⬇️

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