feat: add event listener detection for interaction commands

[szymdzum]

Summary

Add automatic event listener detection to help agents identify interactive elements. Follows "just works" philosophy - validates at interaction time, not discovery.

Problem

Agents clicking non-interactive elements is a common failure mode:

bdg dom query "button"        # Found 5 buttons
bdg dom click --index 2       # Nothing happens... why?
# Was it disabled? Wrong button? No handler attached?

No visibility into whether elements actually have handlers.

Solution

1. Auto-warn on interaction commands (default behavior)

bdg dom click --index 0
# ⚠ No click handlers detected on element
# Clicked button.cancel

• Validate at interaction time (single element = fast)
• Warn but don't fail - sometimes you need to click anyway
• Applies to: click, fill, submit

2. Include listeners in dom get inspection

bdg dom get 0
# ... existing output ...
# events: ["click", "mouseenter"]

Single element inspection = want full details.

3. Add --interactive filter for queries

bdg dom query "button" --interactive
# Only returns elements with handlers

Opt-in filter when specifically looking for clickable elements.

Implementation Notes

• Use DOM.resolveNode to get objectId, then DOMDebugger.getEventListeners
• Keep dom query fast by default (no listener checks)
• Consider checking immediate parent for delegated events
• New exit code not needed (warn only, still succeeds)

Design Principles

• Validate at interaction, not discovery - warning appears exactly when useful
• No extra flags needed for common case
• No performance hit on queries
• Warn, don't fail - agent can proceed if needed

References

• Roadmap: docs/roadmap/ROADMAP.md section 1.5
• CDP method: DOMDebugger.getEventListeners