feat(code): CLI client with gRPC connection + local tools

phase 3 client core:
- sunbeam code subcommand with project discovery, config loading
- gRPC client connects to Sol, starts bidirectional session
- 7 client-side tool executors: file_read, file_write, search_replace,
  grep, bash, list_directory
- project context: .sunbeam/prompt.md, .sunbeam/config.toml, git info
- tool permission config (always/ask/never per tool)
- simple stdin loop (ratatui TUI in phase 4)
- aligned sunbeam-proto to tonic 0.14

sunbeam/src/cli.rs

@@ -139,6 +139,12 @@ pub enum Verb {
         action: Option<PmAction>,
     },
 
+    /// Terminal coding agent powered by Sol.
+    Code {
+        #[command(subcommand)]
+        action: Option<crate::code::CodeCommand>,
+    },
+
     /// Self-update from latest mainline commit.
     Update,
 
@@ -1053,6 +1059,8 @@ pub async fn dispatch() -> Result<()> {
             }
         },
 
+        Some(Verb::Code { action }) => crate::code::cmd_code(action).await,
+
         Some(Verb::Update) => sunbeam_sdk::update::cmd_update().await,
 
         Some(Verb::Version) => {