Add history pruning with configurable max entries and max days

- Add history_max_entries (default 50) and history_max_days (default 30)
  to AppConfig
- Add prune() method to HistoryStore that removes old entries by age
  and count limits
- Call prune after each history entry is added in the GUI
- Preserve history settings through settings dialog save/load cycle

pixstrip-core/src/config.rs

@@ -17,6 +17,8 @@ pub struct AppConfig {
     pub high_contrast: bool,
     pub large_text: bool,
     pub reduced_motion: bool,
+    pub history_max_entries: usize,
+    pub history_max_days: u32,
 }
 
 impl Default for AppConfig {
@@ -36,6 +38,8 @@ impl Default for AppConfig {
             high_contrast: false,
             large_text: false,
             reduced_motion: false,
+            history_max_entries: 50,
+            history_max_days: 30,
         }
     }
 }

pixstrip-core/src/storage.rs

@@ -272,6 +272,32 @@ impl HistoryStore {
         self.write_all(&entries)
     }
 
+    pub fn prune(&self, max_entries: usize, max_days: u32) -> Result<()> {
+        let mut entries = self.list()?;
+        if entries.is_empty() {
+            return Ok(());
+        }
+
+        let now_secs = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_secs();
+        let cutoff_secs = now_secs.saturating_sub(max_days as u64 * 86400);
+
+        // Remove entries older than max_days
+        entries.retain(|e| {
+            e.timestamp.parse::<u64>().unwrap_or(0) >= cutoff_secs
+        });
+
+        // Trim to max_entries (keep the most recent)
+        if entries.len() > max_entries {
+            let start = entries.len() - max_entries;
+            entries = entries.split_off(start);
+        }
+
+        self.write_all(&entries)
+    }
+
     pub fn list(&self) -> Result<Vec<HistoryEntry>> {
         if !self.history_path.exists() {
             return Ok(Vec::new());

pixstrip-gtk/src/app.rs

@@ -1629,6 +1629,11 @@ fn show_results(
         output_files,
     });
 
+    // Prune old history entries
+    let config_store = pixstrip_core::storage::ConfigStore::new();
+    let app_config = config_store.load().unwrap_or_default();
+    let _ = history.prune(app_config.history_max_entries, app_config.history_max_days);
+
     // Show toast
     let savings = if result.total_input_bytes > 0 {
         let pct =

pixstrip-gtk/src/settings.rs

@@ -271,6 +271,10 @@ pub fn build_settings_dialog() -> adw::PreferencesDialog {
         });
     }
 
+    // Preserve history settings from current config (not exposed in UI yet)
+    let hist_max_entries = config.history_max_entries;
+    let hist_max_days = config.history_max_days;
+
     // Save settings when the dialog closes
     dialog.connect_closed(move |_| {
         let new_config = AppConfig {
@@ -305,6 +309,8 @@ pub fn build_settings_dialog() -> adw::PreferencesDialog {
             high_contrast: contrast_row.is_active(),
             large_text: large_text_row.is_active(),
             reduced_motion: motion_row.is_active(),
+            history_max_entries: hist_max_entries,
+            history_max_days: hist_max_days,
         };
 
         let store = ConfigStore::new();