feat!: add structured configuration diagnostics

[m62624]

Summary

• add typed configuration context and stable diagnostics with config path, platform, profile, field, and source location
• render concise CLI configuration errors with insta coverage
• expose the same structured metadata through the Python and Java bindings
• keep macOS executable-runtime decisions in the native backend, with typed read/executable-root failures and a single Seatbelt baseline
• update the relevant specifications and backend/configuration tests

Breaking change

ConfigError variants now carry diagnostic context, and NoDefaultProfile is a struct variant. Consumers matching these variants must account for the new context field.

Verification

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace --all-targets
• Python stub generation, Ruff, mypy, and pytest: 12 passed, 7 skipped
• Gradle test and ktlintCheck

Workflow files and crate versions were not changed.