rewrite planoai CLI in Rust

Add crates/plano-cli/ as a full Rust rewrite of the Python CLI.
Binary name: planoai. All subcommands ported: up, down, build,
logs, cli-agent, trace, init. Config validation and Tera template
rendering replace the Python config_generator. CI updated to use
cargo test/build instead of Python test jobs.

crates/plano-cli/build.rs

@@ -0,0 +1,4 @@
+fn main() {
+    // For now, just rerun if templates change
+    println!("cargo:rerun-if-changed=templates/");
+}