feat: Add initial project structure and dependencies

This commit introduces the foundational elements of the project:
- `.gitignore` file to exclude build artifacts and environment
  variables.
- `Cargo.lock` and `Cargo.toml` defining project dependencies and
  metadata.
- `diesel.toml` for Diesel CLI configuration.
- Initial migration files (`down.sql`, `up.sql`) for database schema
  setup.
- `rustfmt.toml` for code formatting.
- Basic module structure for database, routes, schema, state, and types.
- `src/main.rs` with basic Axum server setup and dotenv loading.
- `src/routes/system_router.rs` for basic API endpoint.
- `src/state.rs` for managing application state and database connection
  pool.
- Type definitions for Subsonic API responses and extensions.

Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "soundsonic"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+diesel = { version = "2.3.6", features = ["sqlite", "r2d2", "returning_clauses_for_sqlite_3_35"] }
+# build libsqlite3 as part of the build process
+# uncomment this line if you run into setup issues
+# libsqlite3-sys = { version = "0.36", features = ["bundled"] }
+dotenvy = "0.15.7"
+axum = "0.8.8"
+serde = { version = "1.0.228", features = ["derive"] }
+serde_json = "1.0.149"
+tokio = { version = "1.49.0", features = ["full"] }
+tracing-subscriber = "0.3.22"