fix: add Helium auto-connect discovery

[hhushhas]

Summary

• add Helium macOS user-data directories to CDP auto-connect discovery
• update the auto-connect error/help/docs to treat Helium as a supported Chromium-based browser
• add a macOS unit test covering Helium discovery paths

Why

Hasan has been using Helium with agent-browser through local workaround docs and manual attach flow. The CDP/session layer already works; the missing piece was first-class discovery and matching user-facing guidance.

Verification

• cargo fmt --manifest-path cli/Cargo.toml -- --check
• cargo clippy --manifest-path cli/Cargo.toml -- -D warnings
• cargo test --manifest-path cli/Cargo.toml -- --skip native::parity_tests::test_all_documented_actions_are_handled
• pnpm install --frozen-lockfile
• pnpm --dir docs build

Notes

• A full cargo test --manifest-path cli/Cargo.toml run hung in native::parity_tests::test_all_documented_actions_are_handled; the targeted run above passed with that single pre-existing hang skipped.