Satisfy latest CI guardrails

[1jehuang]

This PR was originally used for issue #201 validation, but the Windows browser setup fixes are now already on master:

• d4fda75 Require Firefox bridge host asset during setup
• a68185c Use file URLs for browser extension install
• 719b4a5 Always refresh Windows native host registry
• 95db8ae Repair browser setup when native host is missing

After rebasing on current master, this PR only carries unrelated CI guardrail cleanup for newer rustfmt/clippy behavior. It is no longer required to close #201.

[1jehuang]

Superseded. Per this PR's own description, its substantive browser-setup fixes (#201) are already on master. The only remaining content was CI guardrail cleanup for newer rustfmt/clippy, which is now done comprehensively in #419 (full cargo fmt --all, clippy --all-targets --all-features -- -D warnings clean, and refreshed budget baselines) against current master. This branch is also based on a stale tree (its clippy commits target pre-crate-split paths like src/auth/lifecycle.rs), so closing rather than rebasing.