Split CI into app + sidecar workflows, fix reqwest compilation

CI split:
- release.yml: version bump + lightweight app builds (no Python/sidecar)
- build-sidecar.yml: builds CPU + CUDA sidecar variants per platform,
  uploads as separate release assets, runs in parallel with app builds
- Sidecar workflow uses retry loop to find release (race with version bump)

Fixes:
- Add reqwest "json" feature for .json() method
- Add explicit type annotations for reqwest Response and bytes::Bytes
- Reuse client instance for download (was using reqwest::get directly)

Bundle targets: deb, rpm, nsis, msi, dmg (all formats, app is small now)
Windows upload finds both *.msi and *-setup.exe

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

src-tauri/src/commands/sidecar.rs

@@ -84,8 +84,8 @@ pub async fn download_sidecar(app: AppHandle, variant: String) -> Result<(), Str
         ));
     }
 
-    let release_json: serde_json::Value = release_resp
-        .json()
+    let release_json = release_resp
+        .json::<serde_json::Value>()
         .await
         .map_err(|e| format!("Failed to parse release JSON: {}", e))?;
 
@@ -102,7 +102,9 @@ pub async fn download_sidecar(app: AppHandle, variant: String) -> Result<(), Str
         .to_string();
 
     // Stream download with progress events
-    let response = reqwest::get(&download_url)
+    let response: reqwest::Response = client
+        .get(&download_url)
+        .send()
         .await
         .map_err(|e| format!("Failed to start download: {}", e))?;
 
@@ -110,7 +112,7 @@ pub async fn download_sidecar(app: AppHandle, variant: String) -> Result<(), Str
         return Err(format!("Download failed: HTTP {}", response.status()));
     }
 
-    let total = response.content_length().unwrap_or(0);
+    let total: u64 = response.content_length().unwrap_or(0);
     let mut downloaded: u64 = 0;
     let mut stream = response.bytes_stream();
 
@@ -119,7 +121,8 @@ pub async fn download_sidecar(app: AppHandle, variant: String) -> Result<(), Str
         .map_err(|e| format!("Failed to create zip file: {}", e))?;
 
     while let Some(chunk) = stream.next().await {
-        let chunk = chunk.map_err(|e| format!("Download stream error: {}", e))?;
+        let chunk: bytes::Bytes =
+            chunk.map_err(|e| format!("Download stream error: {}", e))?;
         file.write_all(&chunk)
             .map_err(|e| format!("Failed to write chunk: {}", e))?;
         downloaded += chunk.len() as u64;
@@ -188,8 +191,8 @@ pub async fn check_sidecar_update() -> Result<Option<UpdateInfo>, String> {
         ));
     }
 
-    let release_json: serde_json::Value = resp
-        .json()
+    let release_json = resp
+        .json::<serde_json::Value>()
         .await
         .map_err(|e| format!("Failed to parse release JSON: {}", e))?;