fix: audit LOW fixes — docs, rustdoc, scope, debug gate, lto fat (v0.6.12)

- Update CLAUDE.md and README.md to reflect the blur range [0,200] that
  the code has clamped to since v0.6.8.
- Move the // SYNC: comment above the /// doc on MAX_BLUR_DIMENSION so
  rustdoc renders one coherent paragraph instead of a truncated sentence.
- Narrow check_account visibility to pub(crate) and document the caller
  precondition (username must come from users::get_current_user()).
- Gate MOONLOCK_DEBUG behind #[cfg(debug_assertions)]. Release builds
  always run at LevelFilter::Info so a session script cannot escalate
  journal verbosity to leak fprintd / D-Bus internals.
- Document why pam_setcred is deliberately not called in authenticate().
- Release profile: lto = "fat" instead of "thin" — doubles release build
  time for better cross-crate inlining on the auth + i18n hot paths.

Cargo.lock

@@ -575,7 +575,7 @@ dependencies = [
 
 [[package]]
 name = "moonlock"
-version = "0.6.11"
+version = "0.6.12"
 dependencies = [
  "gdk-pixbuf",
  "gdk4",