feat(18-04): Task 1 — Kommandos, Versionsprüfung und Tray für Update/Autostart

- tauri-plugin-opener@2 hinzugefügt (Legitimität in RESEARCH geprüft)
- Neue Rust-Kommandos check_server/save_server_url für die Erststart-Seite,
  Adressen laufen über api_url() ausschließlich über /api-proxy/*
- Versionsprüfung gegen /api-proxy/desktop/latest statt /health/version,
  schaltet den Tray-Eintrag "Update herunterladen" frei und benennt ihn um
- Tray-Menü: Öffnen · Update herunterladen · Autostart-Haken · Beenden,
  echte Umlaute, Update-Eintrag öffnet die Download-Seite im Systembrowser
- capabilities/default.json: opener:allow-open-url für http/https
- cargo check und cargo clippy grün

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

apps/desktop/src-tauri/Cargo.lock

@@ -1820,6 +1820,25 @@ version = "2.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d98f6fed1fde3f8c21bc40a1abb88dd75e67924f9cffc3ef95607bad8017f8e2"
 
+[[package]]
+name = "is-docker"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "928bae27f42bc99b60d9ac7334e3a21d10ad8f1835a4e12ec3ec0464765ed1b3"
+dependencies = [
+ "once_cell",
+]
+
+[[package]]
+name = "is-wsl"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "173609498df190136aa7dea1a91db051746d339e18476eed5ca40521f02d7aa5"
+dependencies = [
+ "is-docker",
+ "once_cell",
+]
+
 [[package]]
 name = "itoa"
 version = "1.0.18"
@@ -2410,6 +2429,17 @@ version = "1.21.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9f7c3e4beb33f85d45ae3e3a1792185706c8e16d043238c593331cc7cd313b50"
 
+[[package]]
+name = "open"
+version = "5.4.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa576c76302b7b808eecc68061e67336c47833ef9d22caa74dda10fa9675eebc"
+dependencies = [
+ "dunce",
+ "is-wsl",
+ "libc",
+]
+
 [[package]]
 name = "openssl"
 version = "0.10.81"
@@ -3818,6 +3848,28 @@ dependencies = [
  "url",
 ]
 
+[[package]]
+name = "tauri-plugin-opener"
+version = "2.5.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "60d60366174b745b4ef5824b8bbc1c457fd08f0ce101ff643c0a49181a9f4e91"
+dependencies = [
+ "dunce",
+ "glob",
+ "objc2-app-kit",
+ "objc2-foundation",
+ "open",
+ "schemars 0.8.22",
+ "serde",
+ "serde_json",
+ "tauri",
+ "tauri-plugin",
+ "thiserror 2.0.18",
+ "url",
+ "windows",
+ "zbus",
+]
+
 [[package]]
 name = "tauri-plugin-store"
 version = "2.4.3"
@@ -3995,6 +4047,7 @@ dependencies = [
  "tauri-build",
  "tauri-plugin-autostart",
  "tauri-plugin-notification",
+ "tauri-plugin-opener",
  "tauri-plugin-store",
  "tauri-plugin-window-state",
 ]