feat: combine slash command jobs into single job steps

[devin-ai-integration]

Use forked slash-command-dispatch with 'dispatched' boolean output

Changes

1. Updated workflow to use Aaron's forked action (aaronsteers/slash-command-dispatch@aj/fix/add-dispatched-bool-output)
2. Combined slash command jobs into steps within a single job for better efficiency
3. Simplified unrecognized command handling using the new 'dispatched' output

Implementation Details

• Using forked action from Aaron's branch that adds the new 'dispatched' boolean output
• The 'dispatched' output indicates whether a slash command was successfully dispatched
• Moved unrecognized command handling into the main job as additional steps
• Simplified conditional logic to use steps.dispatch.outputs.dispatched directly
• Removed unnecessary job outputs since we're using step outputs directly

Testing

This change requires merging to main before it can be tested, as it modifies GitHub Actions workflow configuration.

Link to Devin run: https://app.devin.ai/sessions/19bfcd3c77084c55b445d7ba46e5f65c

[devin-ai-integration]

Original prompt:

@Devin - In the CDK repo, can you modify our slash command dispatch workflow as follows: If someone enters a one-line comment that starts with `/`, let's assume they are trying to enter a slash command. If it doesn't match a supported command (including if they literally type `/help` - then post back a comment to them telling what slash commands are available.

[devin-ai-integration]

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