Add Foundry mobile layout with Tauri iOS/Android support

- Add responsive mobile layout with bottom pill tab bar, swipe navigation, and task list as home screen
- Add platform detection (useIsMobile hook) with viewport breakpoint and VITE_MOBILE build flag
- Mobile-optimize settings/billing/account pages (single-column layout with horizontal tabs)
- Add iOS safe area inset handling with 47px minimum padding
- Scaffold Tauri v2 mobile targets (iOS/Android) with platform-gated sidecar and capabilities
- Add notification sound support and mobile build script

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

foundry/packages/desktop/src-tauri/Cargo.toml

@@ -3,13 +3,20 @@ name = "foundry"
 version = "0.1.0"
 edition = "2021"
 
+[lib]
+crate-type = ["staticlib", "cdylib", "lib"]
+
 [build-dependencies]
 tauri-build = { version = "2", features = [] }
 
 [dependencies]
 tauri = { version = "2", features = [] }
-tauri-plugin-shell = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 reqwest = { version = "0.12", features = ["json"] }
 tokio = { version = "1", features = ["time"] }
+
+# Shell plugin is desktop-only (used for sidecar spawning).
+# Exclude iOS and Android targets.
+[target.'cfg(not(any(target_os = "ios", target_os = "android")))'.dependencies]
+tauri-plugin-shell = "2"