fix(sidecar): probe installed and dev paths for the binary

dpkg-deb -c on the bundled .deb shows mycelium at /usr/bin/mycelium
(no triple suffix), next to the app launcher. Our previous resolver
only looked for the suffixed dev name in resource_dir, so the
installed app could not find its sidecar.

Probe order is now: directory of current_exe, then resource_dir,
then CARGO_MANIFEST_DIR/binaries, then $PATH, with both the plain
"mycelium" name and the dev-style "mycelium-<triple>" alias
checked at each location.

src-tauri/src/sidecar.rs

@@ -295,30 +295,67 @@ fn pick_port_skip(taken: &[u16]) -> AppResult<u16> {
     ))
 }
 
-/// Resolve the bundled `mycelium-<triple>` binary in both `tauri dev`
-/// (cargo manifest) and bundled (resource_dir) modes.
+/// Resolve the bundled `mycelium` sidecar across our two build modes:
+///   • `tauri dev` keeps the file under `src-tauri/binaries/` with the
+///     `-<target_triple>` suffix Tauri's externalBin convention requires.
+///   • `tauri build` for a `.deb` strips the suffix and places the
+///     binary at `/usr/bin/mycelium` next to the app launcher.
+/// We probe the bundled path first, then walk back to the dev location.
 fn locate_sidecar(app: &AppHandle) -> AppResult<PathBuf> {
     let triple = std::env::var("TAURI_ENV_TARGET_TRIPLE")
         .ok()
         .or_else(|| option_env!("TARGET").map(|s| s.to_string()))
         .unwrap_or_else(|| "x86_64-unknown-linux-gnu".to_string());
-    let name = format!("mycelium-{triple}");
+    let suffixed = format!("mycelium-{triple}");
+    let plain = "mycelium".to_string();
     let mut tried: Vec<PathBuf> = Vec::new();
 
+    // Bundled .deb / AppImage: the launcher lives next to the sidecar
+    // under /usr/bin/. Resolve relative to the running executable.
+    if let Ok(exe) = std::env::current_exe() {
+        if let Some(dir) = exe.parent() {
+            for name in [&plain, &suffixed] {
+                let p = dir.join(name);
+                if p.exists() {
+                    return Ok(p);
+                }
+                tried.push(p);
+            }
+        }
+    }
+
+    // Tauri's resource_dir() — used when externalBin is treated as a
+    // resource (older bundles, or when the user moves things around).
     if let Ok(resource) = app.path().resource_dir() {
-        let p = resource.join(&name);
+        for name in [&plain, &suffixed] {
+            let p = resource.join(name);
+            if p.exists() {
+                return Ok(p);
+            }
+            tried.push(p);
+        }
+    }
+
+    // Dev mode: `pnpm tauri dev` runs the binary out of target/debug/ so
+    // current_exe() is far from src-tauri/binaries/. Use the manifest dir.
+    let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    for name in [&suffixed, &plain] {
+        let p = manifest_dir.join("binaries").join(name);
         if p.exists() {
             return Ok(p);
         }
         tried.push(p);
     }
 
-    let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
-    let dev_path = manifest_dir.join("binaries").join(&name);
-    if dev_path.exists() {
-        return Ok(dev_path);
+    // Final fallback: trust $PATH if a system-installed mycelium is around.
+    if let Ok(path) = std::env::var("PATH") {
+        for entry in path.split(':') {
+            let p = PathBuf::from(entry).join(&plain);
+            if p.exists() {
+                return Ok(p);
+            }
+        }
     }
-    tried.push(dev_path);
 
     Err(AppError::SidecarNotFound(tried))
 }

src-tauri/tauri.conf.json

@@ -29,7 +29,7 @@
   "bundle": {
     "active": true,
     "targets": ["deb", "appimage"],
-    "category": "Network",
+    "category": "Utility",
     "shortDescription": "Mycelium overlay network client",
     "longDescription": "Desktop GUI for the Mycelium end-to-end encrypted IPv6 overlay network.",
     "icon": [