feat: phase 2 quick wins (#65 #69 #72)

- #65: update policies + per-agent version pinning
  - add settings.update_policy (stable/latest/skip)
  - add AgentDef.pin_version
  - honor both in update_cmd
  - add update_policy tests

- #69: REPL color theme CLI command
  - add am theme [name] (show/switch)
  - persist selected theme to config

- #72: doctor checks local model runtimes
  - verify ollama and llama-server on PATH
  - for ollama, also check server responds (ollama ls)

Version 0.4.4

src/commands/mod.rs

@@ -28,6 +28,7 @@ pub mod sessions_cmd;
 pub mod stats_cmd;
 pub mod self_update;
 pub mod status_cmd;
+pub mod theme_cmd;
 pub mod timeline_cmd;
 pub mod tip_cmd;
 pub mod uninstall_cmd;
@@ -37,7 +38,7 @@ pub mod version_cmd;
 
 use crate::app::App;
 use crate::cli::Command;
-use crate::config::{AgentDef, MethodSpec};
+use crate::config::{AgentDef, MethodSpec, UpdatePolicy};
 use crate::state::InstalledEntry;
 use anyhow::{anyhow, bail, Result};
 use std::collections::BTreeMap;
@@ -164,6 +165,7 @@ pub fn execute_command(app: &App, cmd: &Command) -> Result<i32> {
         Command::Version => version_cmd::run(app),
         Command::Tip { random } => tip_cmd::run(app, *random),
         Command::Config(sub) => config_cmd::run(app, sub),
+        Command::Theme { name } => theme_cmd::run(app, name.as_deref()),
         Command::Doctor { fix } => doctor_cmd::run(app, *fix),
         Command::Run { agent, args } => run_cmd::run(app, agent, args),
         Command::Completion { shell, installed } => completion_cmd::run(*shell, *installed),