feat(snap): add snap sandbox detection and welcome modal wiring

Detect when QBZ runs inside a Snap sandbox (via SNAP env var) and show
a one-time welcome modal with required plug connection commands. Adds a
Snap Sandbox section in Settings with copyable commands, mirroring the
existing Flatpak pattern.

Backend: snap.rs module, DB table snap_welcome_shown, V2 commands.
Frontend: updatesService, +page.svelte modal queue, SettingsView section.

src-tauri/src/commands_v2.rs

@@ -10449,6 +10449,18 @@ pub fn v2_is_running_in_flatpak() -> bool {
     crate::flatpak::is_running_in_flatpak()
 }
 
+#[tauri::command]
+pub fn v2_is_running_in_snap() -> bool {
+    crate::snap::is_running_in_snap()
+}
+
+#[tauri::command]
+pub fn v2_mark_snap_welcome_shown(
+    state: State<'_, crate::updates::UpdatesState>,
+) -> Result<(), String> {
+    crate::updates::mark_snap_welcome_shown(state)
+}
+
 #[tauri::command]
 pub async fn v2_detect_legacy_cached_files(
     cache_state: State<'_, OfflineCacheState>,

src-tauri/src/lib.rs

@@ -26,6 +26,7 @@ pub mod config;
 pub mod credentials;
 pub mod discogs;
 pub mod flatpak;
+pub mod snap;
 pub mod lastfm;
 pub mod library;
 pub mod listenbrainz;
@@ -1183,6 +1184,7 @@ pub fn run() {
             flatpak::get_flatpak_help_text,
             config::legal_settings::get_qobuz_tos_accepted,
             updates::has_flatpak_welcome_been_shown,
+            updates::has_snap_welcome_been_shown,
             lyrics::commands::lyrics_get,
             config::favorites_cache::is_track_favorite,
             commands_v2::v2_set_api_locale,
@@ -1356,6 +1358,8 @@ pub fn run() {
             commands_v2::v2_remote_control_regenerate_token,
             commands_v2::v2_remote_control_get_pairing_qr,
             commands_v2::v2_is_running_in_flatpak,
+            commands_v2::v2_is_running_in_snap,
+            commands_v2::v2_mark_snap_welcome_shown,
             commands_v2::v2_detect_legacy_cached_files,
             commands_v2::v2_reco_log_event,
             commands_v2::v2_reco_train_scores,

src-tauri/src/snap.rs

@@ -0,0 +1,16 @@
+//! Snap runtime detection and utilities
+//!
+//! Detects when QBZ is running inside a Snap sandbox
+//! and provides sandbox-specific guidance.
+
+use std::env;
+
+/// Check if QBZ is running inside a Snap sandbox
+pub fn is_snap() -> bool {
+    env::var("SNAP").is_ok()
+}
+
+#[tauri::command]
+pub fn is_running_in_snap() -> bool {
+    is_snap()
+}

src-tauri/src/updates/mod.rs

@@ -143,6 +143,11 @@ impl UpdatesStore {
             CREATE TABLE IF NOT EXISTS flatpak_welcome_shown (
                 id INTEGER PRIMARY KEY CHECK (id = 1),
                 shown_at INTEGER NOT NULL
+            );
+
+            CREATE TABLE IF NOT EXISTS snap_welcome_shown (
+                id INTEGER PRIMARY KEY CHECK (id = 1),
+                shown_at INTEGER NOT NULL
             );",
         )
         .map_err(|e| format!("Failed to create updates tables: {}", e))?;
@@ -273,6 +278,26 @@ impl UpdatesStore {
             .map_err(|e| format!("Failed to mark flatpak_welcome_shown: {}", e))?;
         Ok(())
     }
+
+    pub fn has_snap_welcome_been_shown(&self) -> bool {
+        self.conn
+            .query_row(
+                "SELECT 1 FROM snap_welcome_shown WHERE id = 1 LIMIT 1",
+                [],
+                |_row| Ok(()),
+            )
+            .is_ok()
+    }
+
+    pub fn mark_snap_welcome_shown(&self) -> Result<(), String> {
+        self.conn
+            .execute(
+                "INSERT OR REPLACE INTO snap_welcome_shown (id, shown_at) VALUES (1, ?1)",
+                params![now_epoch_seconds()],
+            )
+            .map_err(|e| format!("Failed to mark snap_welcome_shown: {}", e))?;
+        Ok(())
+    }
 }
 
 /// Thread-safe state wrapper
@@ -543,6 +568,16 @@ pub fn mark_flatpak_welcome_shown(state: tauri::State<UpdatesState>) -> Result<(
     state.with_store(|store| store.mark_flatpak_welcome_shown())?
 }
 
+#[tauri::command]
+pub fn has_snap_welcome_been_shown(state: tauri::State<UpdatesState>) -> Result<bool, String> {
+    state.with_store(|store| store.has_snap_welcome_been_shown())
+}
+
+#[tauri::command]
+pub fn mark_snap_welcome_shown(state: tauri::State<UpdatesState>) -> Result<(), String> {
+    state.with_store(|store| store.mark_snap_welcome_shown())?
+}
+
 #[tauri::command]
 pub fn get_current_version(state: tauri::State<UpdatesState>) -> String {
     state.current_version()