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-gtk/src/app.rs

@@ -78,6 +78,9 @@ pub struct JobConfig {
     pub rename_counter_start: u32,
     pub rename_counter_padding: u32,
     pub rename_template: String,
+    pub rename_case: u32,        // 0=none, 1=lower, 2=upper, 3=title
+    pub rename_find: String,
+    pub rename_replace: String,
     // Output
     pub preserve_dir_structure: bool,
     pub overwrite_behavior: u8,
@@ -389,6 +392,9 @@ fn build_ui(app: &adw::Application) {
             rename_counter_start: 1,
             rename_counter_padding: 3,
             rename_template: String::new(),
+            rename_case: 0,
+            rename_find: String::new(),
+            rename_replace: String::new(),
             preserve_dir_structure: false,
             overwrite_behavior: match app_cfg.overwrite_behavior {
                 pixstrip_core::config::OverwriteBehavior::Ask => 0,
@@ -1847,6 +1853,9 @@ fn run_processing(_window: &adw::ApplicationWindow, ui: &WizardUi) {
             } else {
                 Some(cfg.rename_template.clone())
             },
+            case_mode: cfg.rename_case,
+            regex_find: cfg.rename_find.clone(),
+            regex_replace: cfg.rename_replace.clone(),
         });
     }
 
@@ -2786,6 +2795,9 @@ fn build_preset_from_config(cfg: &JobConfig, name: &str) -> pixstrip_core::prese
             } else {
                 Some(cfg.rename_template.clone())
             },
+            case_mode: cfg.rename_case,
+            regex_find: cfg.rename_find.clone(),
+            regex_replace: cfg.rename_replace.clone(),
         })
     } else {
         None