fix(browser): return MEDIA: path from screenshot for channel delivery

[xthanhn91]

Summary

• handleScreenshot returned a truncated base64 string (first 100 chars of encoded data), effectively discarding the screenshot bytes
• The media pipeline in loop.go requires MEDIA: prefix in tool results to collect files for channel delivery (e.g. sendPhoto on Telegram) — without it, screenshots were silently lost
• Save screenshot bytes to a temp file and return MEDIA:/path, matching the pattern used by create_image and tts tools

Root Cause

// Before: truncated base64 text, no MEDIA: prefix → never delivered
encoded := base64.StdEncoding.EncodeToString(data)
return tools.NewResult(fmt.Sprintf("Screenshot captured (%d bytes). Base64: %s",
    len(data), encoded[:min(100, len(encoded))]))

parseMediaResult() in loop.go scans tool output for MEDIA: prefix to route files to channel delivery. Without this prefix, the screenshot was only returned as meaningless truncated text to the LLM.

Fix

// After: save to file + return MEDIA: path → delivered via sendPhoto/sendDocument
imagePath := filepath.Join(os.TempDir(), fmt.Sprintf("goclaw_screenshot_%d.png", time.Now().UnixNano()))
os.WriteFile(imagePath, data, 0644)
return &tools.Result{ForLLM: fmt.Sprintf("MEDIA:%s", imagePath)}

Test plan

• Start browser → open URL → take screenshot → verify image delivered to Telegram/Discord
• Verify temp file cleanup by dispatchOutbound after delivery
• Verify fullPage: true screenshots also work