Wire resize algorithm selection, overwrite behavior, and fix rotation/flip scope

- Add ResizeAlgorithm enum (Lanczos3/CatmullRom/Bilinear/Nearest) to core
- Thread algorithm selection from UI ComboRow through ProcessingJob to resize_image
- Add OverwriteBehavior enum (AutoRename/Overwrite/Skip) to core
- Implement overwrite handling in executor with auto-rename suffix logic
- Wire overwrite behavior from output step through to processing job
- Fix rotation/flip to apply when resize step is enabled, not just adjustments

pixstrip-core/src/operations/mod.rs

@@ -46,6 +46,22 @@ impl ResizeConfig {
     }
 }
 
+// --- Resize Algorithm ---
+
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+pub enum ResizeAlgorithm {
+    Lanczos3,
+    CatmullRom,
+    Bilinear,
+    Nearest,
+}
+
+impl Default for ResizeAlgorithm {
+    fn default() -> Self {
+        Self::Lanczos3
+    }
+}
+
 // --- Rotation / Flip ---
 
 #[derive(Debug, Clone, Copy, Serialize, Deserialize)]
@@ -225,6 +241,21 @@ impl AdjustmentsConfig {
     }
 }
 
+// --- Overwrite Behavior ---
+
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+pub enum OverwriteBehavior {
+    AutoRename,
+    Overwrite,
+    Skip,
+}
+
+impl Default for OverwriteBehavior {
+    fn default() -> Self {
+        Self::AutoRename
+    }
+}
+
 // --- Rename ---
 
 #[derive(Debug, Clone, Serialize, Deserialize)]