Restrict E2B sandbox to agents only - improve modal specificity

Changes:
- E2B Sandbox section now only appears for agent components
- Commands, MCPs, settings, hooks, and templates no longer show E2B option
- This aligns with the CLI implementation where --sandbox only works with --agent
- Keeps modal clean and relevant for each component type

Reasoning:
E2B sandbox execution is specifically designed for agent workflows since
agents provide the AI decision-making needed for complex cloud operations.
Other component types (commands, settings, etc.) are configuration-based
and don't require isolated execution environments.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: davila7

docs/js/modal-helpers.js

@@ -113,6 +113,7 @@ function createComponentModalHTML(component) {
                                 </div>
                             </div>` : ''}
                             
+                            ${component.type === 'agent' ? `
                             <!-- Run in E2B Sandbox (Cloud Execution) -->
                             <div class="e2b-sandbox-section">
                                 <h4>☁️ Run in E2B Sandbox (Cloud Execution) <span class="new-badge">NEW</span></h4>
@@ -152,7 +153,7 @@ function createComponentModalHTML(component) {
                                         </a>
                                     </div>
                                 </div>
-                            </div>
+                            </div>` : ''}
                         </div>
 
                         <div class="component-content">