feat: add Dockerfile + --host flag for containerized deployment

Adds a multi-stage Dockerfile (rust:1-slim-bookworm builder → distroless/cc
runtime) plus a --host flag for obscura serve that defaults to 127.0.0.1
for safety but can be set to 0.0.0.0 so the container's port is reachable
via docker run -p mapping.

Dockerfile cherry-picked from #84. The SPA chunk loading commit from that
PR was left out — verified it didn't actually fix the Next.js webpack
errors on kiwi.com (#86).

crates/obscura-cdp/src/lib.rs

@@ -3,4 +3,4 @@ pub mod dispatch;
 pub mod types;
 pub mod domains;
 
-pub use server::{start, start_with_full_options, start_with_options};
+pub use server::{start, start_with_full_options, start_with_host, start_with_options};