feat(cli): add --no-auto-memory flag to disable memory reminder in agent mode

Adds a flag to disable the automatic memory update reminder that runs
at the end of agent mode. Useful when running agents that should not
modify project memory.

crates/g3-cli/src/cli_args.rs

@@ -118,4 +118,8 @@ pub struct Cli {
     /// Include additional prompt content from a file (appended before memory)
     #[arg(long, value_name = "PATH")]
     pub include_prompt: Option<PathBuf>,
+
+    /// Disable automatic memory update reminder at end of agent mode
+    #[arg(long)]
+    pub no_auto_memory: bool,
 }