refactor: remove dead agent binding step from add gateway wizard

[aidandaly24]

Description

Remove the dead "Agents" binding step from the add gateway wizard. The step allowed selecting agents to attach to a gateway, but the selection was never used — config.agents was collected in the UI but never read by createGatewayFromWizard or any downstream code. Also removes the --agents CLI flag which was equally a no-op.

Changes:

• Remove agents step from gateway wizard flow (Name → Authorizer → Confirm)
• Remove agents from AddGatewayConfig type and default config
• Remove setAgents callback and agent multi-select navigation
• Remove availableAgents prop from AddGatewayScreen and AddGatewayFlow
• Remove --agents CLI flag from add gateway command
• Clean up step labels and help text

Related Issue

Closes #

Documentation PR

N/A

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe): Dead code removal

Testing

How have you tested the change?

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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