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/rename.rs

@@ -149,6 +149,43 @@ fn is_leap(year: u64) -> bool {
     (year % 4 == 0 && year % 100 != 0) || year % 400 == 0
 }
 
+/// Apply case conversion to a filename (without extension)
+/// case_mode: 0=none, 1=lowercase, 2=uppercase, 3=title case
+pub fn apply_case_conversion(name: &str, case_mode: u32) -> String {
+    match case_mode {
+        1 => name.to_lowercase(),
+        2 => name.to_uppercase(),
+        3 => {
+            // Title case: capitalize first letter of each word (split on _ - space)
+            name.split(|c: char| c == '_' || c == '-' || c == ' ')
+                .map(|word| {
+                    let mut chars = word.chars();
+                    match chars.next() {
+                        Some(first) => {
+                            let upper: String = first.to_uppercase().collect();
+                            upper + &chars.as_str().to_lowercase()
+                        }
+                        None => String::new(),
+                    }
+                })
+                .collect::<Vec<_>>()
+                .join("_")
+        }
+        _ => name.to_string(),
+    }
+}
+
+/// Apply regex find-and-replace on a filename
+pub fn apply_regex_replace(name: &str, find: &str, replace: &str) -> String {
+    if find.is_empty() {
+        return name.to_string();
+    }
+    match regex::Regex::new(find) {
+        Ok(re) => re.replace_all(name, replace).into_owned(),
+        Err(_) => name.to_string(),
+    }
+}
+
 pub fn resolve_collision(path: &Path) -> PathBuf {
     if !path.exists() {
         return path.to_path_buf();