chore(core): clean up Plan 1A clippy warnings

Auto-deref at &Zeroizing<[u8;32]> call sites, range pattern in generators,
useless String::into conversions in tests, unused Zeroizing import.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/idfoto-core/src/generators.rs

@@ -76,7 +76,7 @@ pub fn generate_passphrase(req: &GeneratorRequest) -> Result<Zeroizing<String>>
 }
 
 fn bip39_passphrase(word_count: u32, separator: &str, cap: Capitalization) -> Result<Zeroizing<String>> {
-    if !matches!(word_count, 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12) {
+    if !matches!(word_count, 3..=12) {
         return Err(IdfotoError::Format("word_count must be 3..=12".into()));
     }
     // bip39 v2 requires entropy 128–256 bits in multiples of 32 bits (4 bytes).