refactor(proxy): replace panic-prone unwrap/expect with safe patterns

Harden the proxy module against panics by removing optimistic
unwrap()/expect() calls in favor of pattern matching and graceful
fallbacks:

- copilot_optimizer/cache_injector: bind Value::Array/String directly
  instead of is_array()+as_array().unwrap(); use is_none_or and in-place
  string mutation
- hyper_client: gate the raw-write path with if-let + filter instead of
  has_cases + unwrap()
- gemini_shadow: recover poisoned RwLock via into_inner() rather than
  panicking, with warn logging
- streaming_codex_chat: replace expect("tool state exists") with
  let-else (return/continue)
- merge_tool_results: early-return when messages is absent
- sse: fall back to from_utf8_lossy on the UTF-8 boundary slice

No behavior change on the happy path; all proxy tests pass.

src-tauri/src/proxy/hyper_client.rs

@@ -250,18 +250,14 @@ pub async fn send_request(
         proxy_url,
     );
 
-    if has_cases {
+    if let Some(original_cases) = original_cases
+        .as_ref()
+        .filter(|cases| !cases.cases.is_empty())
+    {
         // Primary path: use raw write + hyper handshake for exact header casing
         let result = tokio::time::timeout(
             timeout,
-            send_raw_request(
-                &uri,
-                &method,
-                &headers,
-                original_cases.as_ref().unwrap(),
-                &body,
-                proxy_url,
-            ),
+            send_raw_request(&uri, &method, &headers, original_cases, &body, proxy_url),
         )
         .await
         .map_err(|_| ProxyError::Timeout(format!("请求超时: {}s", timeout.as_secs())))?;