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-cli/src/main.rs

@@ -326,6 +326,9 @@ fn cmd_process(args: CmdProcessArgs) {
             counter_start: 1,
             counter_padding: 3,
             template: args.rename_template,
+            case_mode: 0,
+            regex_find: String::new(),
+            regex_replace: String::new(),
         });
     }