feat: add batch command for multi-step workflows (#865)

Add `batch` command that reads a JSON array of commands from stdin
and executes them sequentially against the daemon. This avoids
per-command process startup overhead when AI agents run multi-step
browser workflows.

Supports --bail to stop on first error (default: continue all)
and --json for structured output as an array of results.

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -187,6 +187,25 @@ agent-browser wait "#spinner" --state hidden
 
 **Load states:** `load`, `domcontentloaded`, `networkidle`
 
+### Batch Execution
+
+Execute multiple commands in a single invocation by piping a JSON array of
+string arrays to `batch`. This avoids per-command process startup overhead
+when running multi-step workflows.
+
+```bash
+# Pipe commands as JSON
+echo '[
+  ["open", "https://example.com"],
+  ["snapshot", "-i"],
+  ["click", "@e1"],
+  ["screenshot", "result.png"]
+]' | agent-browser batch --json
+
+# Stop on first error
+agent-browser batch --bail < commands.json
+```
+
 ### Clipboard
 
 ```bash