Simplify project and platform build boundaries

[enfipy]

Closes #189.

Summary

• separate deterministic project-config parsing from environment resolution
• share Cargo project discovery, package roots, and path resolution between builds and doctor
• rename ambiguous Config and CrossbowMetadata concepts without compatibility aliases
• consolidate native APK/AAB preparation and split Android build/doctor code by concrete domain
• use published android-manifest 0.4.0 and remove the Boolean/XML compatibility heuristics
• remove YaSerde entirely from the dependency graph
• replace deprecated home-directory lookup and targeted production panic paths

Android manifest verification

The Crossbow regressions pass directly against android-manifest 0.4.0:

• native Boolean wrapper deserialization
• XML attributes containing ampersands, angle brackets, quotes, Unicode, and literal entity text
• one-layer serialization plus parsed-value round trip

Validation

• cargo fmt --all -- --check
• strict Clippy with tests for no features, Android, Apple, and all features
• 89 crossbundle-tools unit tests passed; one Android-SDK-dependent test filtered on this host
• 14 crossbundle CLI unit tests passed
• cargo_metadata, doctor_cli, and update_command integrations passed
• crossbundle and crossbundle-tools doctests passed

The complete workspace all-feature build reaches the existing Linux host boundary in the Apple-only objc2 dependency; package-level platform matrices are clean.