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/archive.rs

@@ -0,0 +1,2 @@
+// Pack, unpack, and inspect archive orchestration.
+// Will be implemented in Plan 02-02.

src/cli.rs

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+use clap::{Parser, Subcommand};
+use std::path::PathBuf;
+
+#[derive(Parser)]
+#[command(name = "encrypted_archive")]
+#[command(about = "Custom encrypted archive tool")]
+pub struct Cli {
+    #[command(subcommand)]
+    pub command: Commands,
+}
+
+#[derive(Subcommand)]
+pub enum Commands {
+    /// Pack files into an encrypted archive
+    Pack {
+        /// Input files to archive
+        #[arg(required = true)]
+        files: Vec<PathBuf>,
+        /// Output archive file
+        #[arg(short, long)]
+        output: PathBuf,
+        /// Disable compression for specified file patterns
+        #[arg(long)]
+        no_compress: Vec<String>,
+    },
+    /// Unpack an encrypted archive
+    Unpack {
+        /// Archive file to unpack
+        archive: PathBuf,
+        /// Output directory
+        #[arg(short, long, default_value = ".")]
+        output_dir: PathBuf,
+    },
+    /// Inspect archive metadata without decrypting
+    Inspect {
+        /// Archive file to inspect
+        archive: PathBuf,
+    },
+}

src/compression.rs

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+// Gzip compression/decompression and compression heuristic.
+// Will be implemented in Task 2.

src/crypto.rs

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+// Cryptographic operations: AES-256-CBC, HMAC-SHA-256, SHA-256.
+// Will be implemented in Task 2.

src/format.rs

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+// Binary format types and serialization/deserialization.
+// Will be implemented in Task 2.

src/key.rs

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+/// Hardcoded 32-byte AES-256 key.
+/// Same key is used for AES-256-CBC encryption and HMAC-SHA-256 authentication (v1).
+/// v2 will derive separate subkeys using HKDF.
+pub const KEY: [u8; 32] = [
+    0x7A, 0x35, 0xC1, 0xD9, 0x4F, 0xE8, 0x2B, 0x6A,
+    0x91, 0x0D, 0xF3, 0x58, 0xBC, 0x74, 0xA6, 0x1E,
+    0x42, 0x8F, 0xD0, 0x63, 0xE5, 0x17, 0x9B, 0x2C,
+    0xFA, 0x84, 0x06, 0xCD, 0x3E, 0x79, 0xB5, 0x50,
+];

src/main.rs

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+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(())
+        }
+    }
+}