Fix bugs across all crates

pixstrip-core/src/operations/mod.rs

@@ -120,6 +120,11 @@ impl ConvertConfig {
             }
         }
     }
+
+    /// Returns true if this conversion will change at least some file extensions.
+    pub fn changes_extension(&self) -> bool {
+        !matches!(self, Self::KeepOriginal)
+    }
 }
 
 // --- Compress ---
@@ -318,6 +323,18 @@ pub struct RenameConfig {
 fn default_counter_position() -> u32 { 3 }
 
 impl RenameConfig {
+    /// Returns true if this rename config would actually change any filename.
+    pub fn changes_filename(&self) -> bool {
+        !self.prefix.is_empty()
+            || !self.suffix.is_empty()
+            || self.counter_enabled
+            || !self.regex_find.is_empty()
+            || self.case_mode > 0
+            || self.replace_spaces > 0
+            || self.special_chars > 0
+            || self.template.is_some()
+    }
+
     /// Pre-compile the regex for batch use. Call once before a loop of apply_simple_compiled.
     pub fn compile_regex(&self) -> Option<regex::Regex> {
         rename::compile_rename_regex(&self.regex_find)