Fix pipeline order, add selective metadata stripping, rename case/regex

- Move watermark step after compress in processing pipeline to match
  design doc order (resize, adjustments, convert, compress, metadata,
  watermark, rename)
- Implement selective EXIF metadata stripping for Privacy and Custom
  modes using little_exif tag filtering (GPS, camera, software,
  timestamps, copyright categories)
- Add case conversion support to rename (none/lower/upper/title)
- Add regex find-and-replace on original filenames
- Wire case and regex controls in rename step UI to JobConfig
- Add regex crate dependency to pixstrip-core

pixstrip-core/src/operations/mod.rs

@@ -279,6 +279,10 @@ pub struct RenameConfig {
     pub counter_start: u32,
     pub counter_padding: u32,
     pub template: Option<String>,
+    /// 0=none, 1=lowercase, 2=uppercase, 3=title case
+    pub case_mode: u32,
+    pub regex_find: String,
+    pub regex_replace: String,
 }
 
 impl RenameConfig {
@@ -290,18 +294,23 @@ impl RenameConfig {
             width = self.counter_padding as usize
         );
 
+        // Apply regex find-and-replace on the original name
+        let working_name = rename::apply_regex_replace(original_name, &self.regex_find, &self.regex_replace);
+
         let mut name = String::new();
         if !self.prefix.is_empty() {
             name.push_str(&self.prefix);
         }
-        name.push_str(original_name);
+        name.push_str(&working_name);
         if !self.suffix.is_empty() {
             name.push_str(&self.suffix);
         }
         name.push('_');
         name.push_str(&counter_str);
-        name.push('.');
-        name.push_str(extension);
-        name
+
+        // Apply case conversion
+        let name = rename::apply_case_conversion(&name, self.case_mode);
+
+        format!("{}.{}", name, extension)
     }
 }