docs: comprehensive Android CI coverage investigation report

Documents all attempts to implement code coverage for Android CI,
including:
- 7 different Swift version attempts
- LLVM version mismatch root cause analysis
- Android SDK artifactbundle investigation
- Short-term and long-term solution recommendations

This report can be shared with the Skip team to help resolve the
LLVM v9/v10 incompatibility between Android SDK and host toolchains.

Key findings:
- Android SDK generates LLVM v9 profraw files
- All modern Swift versions (6.1.1+) have LLVM v10 tools
- Android SDK artifactbundle does not include llvm-profdata/llvm-cov
- Swift 6.1.1 is missing libclang_rt.profile runtime library

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: leogdion