fix(security): add server-side URL scheme validation for roaster homepage

Reject non-http(s) URL schemes (javascript:, data:, etc.) in both
NewRoaster::normalize() and new UpdateRoaster::normalize(). The HTML
input type="url" provides browser-side validation, but the API path
had no server-side check.

src/application/routes/api/roasters.rs

@@ -96,6 +96,7 @@ pub(crate) async fn update_roaster(
     Path(id): Path<RoasterId>,
     Json(payload): Json<UpdateRoaster>,
 ) -> Result<Json<Roaster>, ApiError> {
+    let payload = payload.normalize();
     let has_changes = payload.name.is_some()
         || payload.country.is_some()
         || payload.city.is_some()

src/domain/roasters.rs

@@ -29,7 +29,8 @@ impl NewRoaster {
         self.name = self.name.trim().to_string();
         self.country = self.country.trim().to_string();
         self.city = normalize_optional_field(self.city);
-        self.homepage = normalize_optional_field(self.homepage);
+        self.homepage =
+            normalize_optional_field(self.homepage).filter(|url| is_valid_url_scheme(url));
         self
     }
 
@@ -53,6 +54,13 @@ fn normalize_optional_field(value: Option<String>) -> Option<String> {
     })
 }
 
+/// Returns `true` if the URL starts with `http://` or `https://`.
+/// Rejects `javascript:`, `data:`, and other potentially dangerous schemes.
+fn is_valid_url_scheme(url: &str) -> bool {
+    let lower = url.trim().to_lowercase();
+    lower.starts_with("http://") || lower.starts_with("https://")
+}
+
 impl Roaster {
     pub fn to_timeline_event(&self) -> NewTimelineEvent {
         let mut details = vec![TimelineEventDetail {
@@ -88,6 +96,23 @@ pub struct UpdateRoaster {
     pub homepage: Option<String>,
 }
 
+impl UpdateRoaster {
+    pub fn normalize(mut self) -> Self {
+        self.homepage = self
+            .homepage
+            .and_then(|h| {
+                let trimmed = h.trim().to_string();
+                if trimmed.is_empty() {
+                    None
+                } else {
+                    Some(trimmed)
+                }
+            })
+            .filter(|url| is_valid_url_scheme(url));
+        self
+    }
+}
+
 #[derive(Debug, Clone, Copy, Eq, PartialEq)]
 pub enum RoasterSortKey {
     CreatedAt,