Add font family selector for watermark text

pixstrip-core/src/operations/watermark.rs

@@ -46,7 +46,8 @@ pub fn apply_watermark(
             font_size,
             opacity,
             color,
-        } => apply_text_watermark(img, text, *position, *font_size, *opacity, *color),
+            font_family,
+        } => apply_text_watermark(img, text, *position, *font_size, *opacity, *color, font_family.as_deref()),
         WatermarkConfig::Image {
             path,
             position,
@@ -56,7 +57,38 @@ pub fn apply_watermark(
     }
 }
 
-fn find_system_font() -> Result<Vec<u8>> {
+fn find_system_font(family: Option<&str>) -> Result<Vec<u8>> {
+    // If a specific font family was requested, try to find it via fontconfig
+    if let Some(name) = family {
+        if !name.is_empty() {
+            // Try common font paths with the family name
+            let search_dirs = [
+                "/usr/share/fonts",
+                "/usr/local/share/fonts",
+            ];
+            let name_lower = name.to_lowercase();
+            for dir in &search_dirs {
+                if let Ok(entries) = walkdir(std::path::Path::new(dir)) {
+                    for path in entries {
+                        let file_name = path.file_name()
+                            .and_then(|n| n.to_str())
+                            .unwrap_or("")
+                            .to_lowercase();
+                        if file_name.contains(&name_lower)
+                            && (file_name.ends_with(".ttf") || file_name.ends_with(".otf"))
+                            && (file_name.contains("regular") || !file_name.contains("bold") && !file_name.contains("italic"))
+                        {
+                            if let Ok(data) = std::fs::read(&path) {
+                                return Ok(data);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    // Fall back to default system fonts
     let candidates = [
         "/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf",
         "/usr/share/fonts/TTF/DejaVuSans.ttf",
@@ -78,6 +110,25 @@ fn find_system_font() -> Result<Vec<u8>> {
     })
 }
 
+/// Recursively walk a directory and collect file paths
+fn walkdir(dir: &std::path::Path) -> std::io::Result<Vec<std::path::PathBuf>> {
+    let mut results = Vec::new();
+    if dir.is_dir() {
+        for entry in std::fs::read_dir(dir)? {
+            let entry = entry?;
+            let path = entry.path();
+            if path.is_dir() {
+                if let Ok(sub) = walkdir(&path) {
+                    results.extend(sub);
+                }
+            } else {
+                results.push(path);
+            }
+        }
+    }
+    Ok(results)
+}
+
 fn apply_text_watermark(
     img: DynamicImage,
     text: &str,
@@ -85,8 +136,9 @@ fn apply_text_watermark(
     font_size: f32,
     opacity: f32,
     color: [u8; 4],
+    font_family: Option<&str>,
 ) -> Result<DynamicImage> {
-    let font_data = find_system_font()?;
+    let font_data = find_system_font(font_family)?;
     let font = ab_glyph::FontArc::try_from_vec(font_data).map_err(|_| {
         PixstripError::Processing {
             operation: "watermark".into(),