filters: apply content filters before image-cache URL rewriting

image_cache::process() percent-encodes image URLs into feedthemonkey-img://
scheme URIs (e.g. /thumbs/ becomes %2Fthumbs%2F). Filters applied after
this step can no longer match the original substrings, so a rule like
  www.stuttmann-karikaturen.de  /thumbs/  /
had no effect when image caching was enabled.

Fix by applying filters to the raw article content before passing it to
image_cache::process(), so the corrected URLs are what get encoded into
the cache scheme. The render-time filter pass in load_article_in_webview
remains as a no-op for already-filtered content and still works correctly
for the non-cached code path.

src/window.rs

@@ -648,7 +648,11 @@ pub mod imp {
             let Some(api) = api else { return };
 
             // Reload filter rules on every refresh so edits take effect immediately.
-            *self.filter_rules.borrow_mut() = crate::filters::load_rules();
+            let filter_text = {
+                let settings = gio::Settings::new("net.jeena.FeedTheMonkey");
+                settings.string("content-filters").to_string()
+            };
+            *self.filter_rules.borrow_mut() = crate::filters::parse(&filter_text);
 
             self.refresh_stack.set_visible_child_name("spinner");
             self.content_refresh_stack.set_visible_child_name("spinner");
@@ -675,6 +679,17 @@ pub mod imp {
                         crate::pending_actions::flush(&api, wt).await;
                     }
                     let articles = api.fetch_unread().await?;
+                    // Apply filters before image-cache processing so that rules
+                    // such as /thumbs/ → / rewrite the original URLs before they
+                    // are percent-encoded into feedthemonkey-img:// scheme URIs.
+                    let rules = crate::filters::parse(&filter_text);
+                    let articles: Vec<_> = articles
+                        .into_iter()
+                        .map(|mut a| {
+                            a.content = crate::filters::apply(&rules, &a.id, &a.link, &a.content);
+                            a
+                        })
+                        .collect();
                     let articles = if cache_images {
                         let processed = crate::image_cache::process(articles);
                         crate::runtime::spawn_bg(crate::image_cache::prefetch(processed.clone()));