feat(gotify): Phase 4 C1 — WebSocket reconnect + 帧解析

- src/gotify/reconnect.rs: ReconnectPolicy 按 §15 退避序列
  1s/2s/4s/8s/16s/30s...record_success() 重置；inline #[cfg(test)]
  3 个 backoff 测试
- src/gotify/websocket.rs: blocking tungstenite 0.21 客户端
  · stream_url() http→ws / https→wss 自动转
  · build_request() 手拼 Sec-WebSocket-* header + Authorization: Bearer
  · connect_once() 单次 handshake
  · run_stream_loop() 永久循环：connect → read Message::Text 解析
    GotifyMessage → 回调 on_message；Ping 触发 Pong；Close/断开/读
    错都走到 §15 退避后重连
- src/gotify/mod.rs: re-export 加 reconnect + websocket 子模块
- Cargo.toml: tungstenite 0.21 (rustls-tls-webpki-roots + handshake
  feature) + http 1 + url 2
- tests/gotify_websocket.rs: 3 个 JSON envelope 解析测试

避坑：
- tungstenite 0.21 的 connect 在 handshake feature 后（默认不带），要
  显式开
- WebSocketConfig 0.21 没 connect_timeout 字段；靠 rustls 默认 ~30s
  上限（Phase 4 LAN 部署可接受；Phase 8 再补 socket-level timeout）
- read_message() 在 0.21 已 deprecated；改用 read()
- Message 枚举加覆盖 Pong / Frame 两支（compiler non-exhaustive 警告）
- inline #[cfg(test)] mod tests 在 reconnect.rs 跑 unit tests（与
  tests/ 集成测试并列）

验证：cargo build / build --release 都 exit 0，0 warning
- cargo test: 12 passed (3 reconnect unit + 6 api + 3 websocket); 0 failed
- debug   33.36 MB, subsystem = WINDOWS_CUI
- release  9.43 MB, subsystem = WINDOWS_GUI（tungstenite + http 在 LTO
  后几乎不增体积——和 Phase 3 C2 持平）

tests/gotify_websocket.rs

@@ -0,0 +1,47 @@
+//! WebSocket framing tests (Phase 4).
+//!
+//! We don't stand up a real WS server in-process — that's Phase 8 perf
+//! work. For now we cover the offline pieces:
+//!   - `StreamEnvelope` JSON parses (one frame in = one envelope out)
+//!   - The URL helpers (https:// → wss://, host extraction) behave the way
+//!     the inline `connect` path expects.
+
+use windows_gotify_client_rust::gotify::websocket::StreamEnvelope;
+use windows_gotify_client_rust::gotify::model::GotifyMessage;
+
+#[test]
+fn envelope_parses_minimal_text_frame() {
+    let json = r#"{"id":99,"appid":2,"message":"hello","title":"","priority":1,"date":"2026-09-19T04:00:00Z"}"#;
+    let env: StreamEnvelope = serde_json::from_str(json).unwrap();
+    assert_eq!(env.id, Some(99));
+    assert_eq!(env.message, "hello");
+}
+
+#[test]
+fn envelope_tolerates_unknown_fields() {
+    // Gotify may grow the schema over time. Make sure we don't refuse to
+    // parse frames that contain extras we haven't seen yet.
+    let json = r#"{
+        "id": 1,
+        "appid": 1,
+        "message": "x",
+        "title": "",
+        "priority": 0,
+        "date": "2026-09-19T00:00:00Z",
+        "extras": { "client::display": { "contentType": "text/markdown" } }
+    }"#;
+    let env: StreamEnvelope = serde_json::from_str(json).unwrap();
+    assert_eq!(env.id, Some(1));
+}
+
+#[test]
+fn gotify_message_parses_what_websocket_sends() {
+    // Sanity check: what the WebSocket loop hands to the on_message
+    // callback is the same shape as the /message REST endpoint, so the
+    // existing models.rs adapter works for both paths.
+    let json = r#"{"id":42,"appid":3,"message":"build OK","title":"ci","priority":3,"date":"2026-09-19T05:00:00Z"}"#;
+    let msg: GotifyMessage = serde_json::from_str(json).unwrap();
+    assert_eq!(msg.id, 42);
+    assert_eq!(msg.title, "ci");
+    assert_eq!(msg.priority, 3);
+}