feat: Rust port of Claude Code CLI

Crates:
- api: Anthropic Messages API client with SSE streaming
- tools: Claude-compatible tool implementations (Bash, Read, Write, Edit, Glob, Grep + extended suite)
- runtime: conversation loop, session persistence, permissions, system prompt builder
- rusty-claude-cli: terminal UI with markdown rendering, syntax highlighting, spinners
- commands: subcommand definitions
- compat-harness: upstream TS parity verification

All crates pass cargo fmt/clippy/test.

rust/crates/commands/src/lib.rs

@@ -0,0 +1,29 @@
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CommandManifestEntry {
+    pub name: String,
+    pub source: CommandSource,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CommandSource {
+    Builtin,
+    InternalOnly,
+    FeatureGated,
+}
+
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+pub struct CommandRegistry {
+    entries: Vec<CommandManifestEntry>,
+}
+
+impl CommandRegistry {
+    #[must_use]
+    pub fn new(entries: Vec<CommandManifestEntry>) -> Self {
+        Self { entries }
+    }
+
+    #[must_use]
+    pub fn entries(&self) -> &[CommandManifestEntry] {
+        &self.entries
+    }
+}