Add PR checks pipeline (fmt, clippy, test) and split CI config

- Split .woodpecker.yml into .woodpecker/check.yml (PR checks) and .woodpecker/deploy.yml (deploy on push to main)
- Add basic handler test to src/main.rs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main.rs

@@ -13,3 +13,14 @@ async fn main() {
 async fn handler() -> Html<&'static str> {
     Html("<h1>Mikhail Kilin</h1>")
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn test_handler() {
+        let response = handler().await;
+        assert!(response.0.contains("Mikhail Kilin"));
+    }
+}