fix: improve URL validation with GET fallback for HEAD method errors

some servers (like bsky.app) return HTTP 405 for HEAD requests but work fine with GET. this commit adds a fallback strategy:
- try HEAD first (faster, less bandwidth)
- if HEAD returns error status (405, etc), fall back to GET
- if HEAD fails completely, also try GET
- mark as valid only if either succeeds

this ensures valid URLs aren't incorrectly grayed out while still catching truly invalid domains.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[e-mail]>

src/routes.rs

···
 pub async fn validate_url(query: web::Query<ValidateUrlQuery>) -> HttpResponse {
     let url = &query.url;
 
-    // Try to make a HEAD request with a short timeout
+    // Build client with redirect following and timeout
     let client = reqwest::Client::builder()
         .timeout(std::time::Duration::from_secs(3))
+        .redirect(reqwest::redirect::Policy::limited(5))
         .build()
         .unwrap();
 
+    // Try HEAD first, fall back to GET if HEAD doesn't succeed
     let is_valid = match client.head(url).send().await {
-        Ok(response) => response.status().is_success() || response.status().is_redirection(),
-        Err(_) => false,
+        Ok(response) => {
+            let status = response.status();
+            if status.is_success() || status.is_redirection() {
+                true
+            } else {
+                // HEAD returned error status (like 405), try GET
+                match client.get(url).send().await {
+                    Ok(get_response) => get_response.status().is_success(),
+                    Err(_) => false,
+                }
+            }
+        }
+        Err(_) => {
+            // HEAD request failed completely, try GET as fallback
+            match client.get(url).send().await {
+                Ok(response) => response.status().is_success(),
+                Err(_) => false,
+            }
+        }
     };
 
     HttpResponse::Ok().json(serde_json::json!({