Fix 29 audit findings across all severity tiers

Critical: fix unsquashfs arg order, quote Exec paths with spaces,
fix compare_versions antisymmetry, chunk-based signature detection,
bounded ELF header reads.

High: handle NULL CVE severity, prevent pipe deadlock in inspector,
fix glob_match edge case, fix backup archive path collisions, async
crash detection with stderr capture.

Medium: gate scan on auto-scan setting, fix window size persistence,
fix announce() for Stack containers, claim lightbox gesture, use
serde_json for CLI output, remove dead CSS @media blocks, add
detail-tab persistence, remove invalid metainfo categories, byte-level
fuse signature search.

Low: tighten Wayland env var detection, ELF magic validation,
timeout for update info extraction, quoted arg parsing, stop watcher
timer on window destroy, GSettings choices/range constraints, remove
unused CSS classes, define status-ok/status-attention CSS.

src/i18n.rs

@@ -23,7 +23,6 @@ pub fn i18n_f(msgid: &str, args: &[(&str, &str)]) -> String {
 }
 
 /// Translate a string with singular/plural forms and named placeholders.
-#[allow(dead_code)]
 pub fn ni18n_f(singular: &str, plural: &str, n: u32, args: &[(&str, &str)]) -> String {
     let base = if n == 1 { singular } else { plural };
     let mut result = base.to_string();