Re-enable commented-out lints in workspace config #4

Context: Cargo.toml (soon build/lints.bzl — see prior issue) has these commented with TODO audit:

• arithmetic_side_effects — numeric safety
• indexing_slicing — panic safety
• panic — panic safety
• panic_in_result_fn — panic safety

All four are critical for a kernel.

Scope:

1. Enable each as warn (not deny) in build/lints.bzl.
2. Run just clippy 2>&1 | tee lints.log, count violations per crate.
3. File one follow-up issue per crate titled "Burn down clippy::X in <crate>" with the violation count.
4. As each crate clears, promote the lint to deny via crate-root #![deny(...)].

Acceptance: warnings visible in CI, follow-up issues filed, tracking checklist added to AUDIT.md.