Improve Claude Code provider error message for missing CLI (#3363)

Signed-off-by: deadmanoz <hones02_tunica@icloud.com>
Co-authored-by: Alex Hancock <alexhancock@block.xyz>

crates/goose/src/providers/claude_code.rs

@@ -351,7 +351,11 @@ impl ClaudeCodeProvider {
 
         let mut child = cmd
             .spawn()
-            .map_err(|e| ProviderError::RequestFailed(format!("Failed to spawn command: {}", e)))?;
+            .map_err(|e| ProviderError::RequestFailed(format!(
+                "Failed to spawn Claude CLI command '{}': {}. \
+                Make sure the Claude Code CLI is installed and in your PATH, or set CLAUDE_CODE_COMMAND in your config to the correct path.",
+                self.command, e
+            )))?;
 
         let stdout = child
             .stdout