android: add Tauri v2 shell with GPS tracking for cardio workouts

Wraps the web app in a Tauri Android shell that provides native GPS
via the geolocation plugin. Includes foreground service for background
tracking, live map display, GPS data storage in workout sessions,
and route visualization in workout history.

src-tauri/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "bocken-fitness"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+name = "bocken_fitness_lib"
+crate-type = ["lib", "cdylib", "staticlib"]
+
+[build-dependencies]
+tauri-build = { version = "2", features = [] }
+
+[dependencies]
+tauri = { version = "2", features = [] }
+tauri-plugin-geolocation = "2"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"