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>

Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "encrypted_archive"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+aes = "0.8"
+cbc = "0.1"
+hmac = "0.12"
+sha2 = "0.10"
+flate2 = "1.1"
+clap = { version = "4.5", features = ["derive"] }
+rand = "0.9"
+anyhow = "1.0"