Initial commit: APT-DNF Bridge workspace

- Core crate: Minimal shell-out implementation
- Advanced crate: Pluggable backends and enhanced features
- Main crate: Re-exports core + optional advanced features
- Feature flags: Users choose complexity level
- Examples: Working demonstrations of both approaches
- Documentation: Clear README explaining the structure

Implements the refined two-crate approach with workspace + feature flags.

Cargo.toml

@@ -0,0 +1,23 @@
+[workspace]
+members = [
+    "apt-dnf-bridge-core",
+    "apt-dnf-bridge",
+    "apt-dnf-bridge-advanced",
+]
+resolver = "2"
+
+[workspace.package]
+version = "0.1.0"
+edition = "2021"
+license = "MIT"
+repository = "https://github.com/your-org/apt-dnf-bridge"
+keywords = ["apt", "dnf", "package-manager", "ostree", "bridge"]
+categories = ["os::linux-apis", "development-tools::build-utils"]
+
+[workspace.dependencies]
+anyhow = "1.0"
+async-trait = "0.1"
+serde = { version = "1.0", features = ["derive"] }
+thiserror = "1.0"
+tokio = { version = "1.0", features = ["process", "macros"] }
+tempfile = "3.0"