feat(02-01): project scaffolding with Cargo, CLI skeleton, and key module

- Initialize Rust project with aes, cbc, hmac, sha2, flate2, clap, rand, anyhow dependencies
- Add clap derive CLI with pack/unpack/inspect subcommands
- Add hardcoded 32-byte AES-256 key constant
- Create stub modules for format, crypto, compression, archive
- All 7 source files in place, cargo build succeeds

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main.rs

@@ -0,0 +1,43 @@
+mod archive;
+mod cli;
+mod compression;
+mod crypto;
+mod format;
+mod key;
+
+use clap::Parser;
+use cli::{Cli, Commands};
+
+fn main() -> anyhow::Result<()> {
+    let cli = Cli::parse();
+
+    match cli.command {
+        Commands::Pack {
+            files,
+            output,
+            no_compress,
+        } => {
+            println!(
+                "Pack: {} files -> {:?} (no_compress: {:?})",
+                files.len(),
+                output,
+                no_compress
+            );
+            println!("Not implemented yet");
+            Ok(())
+        }
+        Commands::Unpack {
+            archive,
+            output_dir,
+        } => {
+            println!("Unpack: {:?} -> {:?}", archive, output_dir);
+            println!("Not implemented yet");
+            Ok(())
+        }
+        Commands::Inspect { archive } => {
+            println!("Inspect: {:?}", archive);
+            println!("Not implemented yet");
+            Ok(())
+        }
+    }
+}