chore: strip audit-ticket prefixes from code comments

Drops the ~60 ticket-prefix comments (CRIT-N, HIGH-N, MED-N, LOW-N,
L-N, M-N, AUDIT-N, PLUTUS-N, "audit fix (date):", "Phase N" labels,
"Adversarial-review fix:") that had accumulated in inline + doc
comments over several audit cycles. Where the surrounding prose
still carried useful WHY context it gets kept and tightened; where
the ticket WAS the comment it gets dropped entirely.

No logic, no renames, no behavior change. Audit history lives in
commit messages and the audits/ tree where it belongs — eternal
comments don't need to mirror it.

Net 138 LOC shorter. 253 tests pass, no new clippy or fmt warnings.

crates/aldabra-core/src/lib.rs

@@ -180,7 +180,6 @@ impl Mnemonic {
         // `xprv_bytes` was moved into normalize_bytes_force3rd, but
         // the stack slot can still hold a copy depending on calling
         // conventions / inlining. Defensive zeroize.
-        // (M-1 audit fix.)
         xprv_bytes.zeroize();
         Ok(RootKey { xprv })
     }