chore(core): fix pre-existing clippy warnings (-D warnings gate)

Resolves pre-existing lint issues in imgsecret.rs, time.rs, totp.rs,
and crypto.rs that blocked the cargo clippy --workspace -D warnings
gate. No logic changes: loop-index → iterator, manual div_ceil →
.div_ceil(), manual range contains → .contains(), auto-deref cleanup.

Also fixes pre-existing warnings in relicario-cli (main.rs, session.rs,
device.rs, gitea.rs, helpers.rs, test helpers): dead_code suppression,
too_many_arguments, literal_with_empty_format_string, manual_char_cmp,
map_or → is_none_or, and repeat().take() → vec! in test helpers.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/relicario-core/src/crypto.rs

@@ -408,7 +408,7 @@ mod tests {
         blob.extend_from_slice(&[0u8; 16]);
 
         let key = Zeroizing::new([0u8; 32]);
-        let err = decrypt(&*key, &blob).expect_err("v1 blob should fail decrypt");
+        let err = decrypt(&key, &blob).expect_err("v1 blob should fail decrypt");
         match err {
             RelicarioError::UnsupportedFormatVersion { found, expected } => {
                 assert_eq!(found, 0x01);