fix(auth): report browser cookie extraction failures

[stockedge]

Problem

When browser cookie extraction fails, suno auth --login discards the underlying error and instructs the user to log in again, making cookie access or decryption failures indistinguishable from an absent Suno session.

Solution

• Preserves each browser's read error, including its cause chain, in the final authentication failure.
• Separately reports successful reads that lack a non-empty Suno __client cookie.
• Retains existing browser fallback, cookie selection, and the config_error / exit-code 2 contract.
• Never exposes cookie values in diagnostics.
• Diagnostic-only: does not alter Chrome encryption support or required permissions.

Validation

Tested on Windows with stable MSVC Rust:

• cargo fmt --check passed.
• cargo test --locked passed (64 unit tests, all integration suites, 135 tests total).
• cargo clippy --locked --all-targets -- -D warnings passed.
• Vendored conformance probe passed against the debug executable in Git Bash using native jq --binary output to avoid CRLF in command names.

Notes:

• The default GNU toolchain cannot build the existing libesedb-sys dependency; the installed MSVC toolchain passes all checks.
• GitHub Actions on this fork awaits maintainer approval; release, Linux, and macOS checks remain for CI.