fix: conditionally show invoke in deploy next steps only when agents exist

[notgitika]

Description

The TUI deploy screen always showed invoke as a next step after deployment, even when no agents were configured (e.g., memory-only projects). This was misleading since there's nothing to invoke without an agent.

Changed DEPLOY_NEXT_STEPS from a static constant to a function getDeployNextSteps(hasAgents) that checks context.projectSpec.agents to determine the appropriate next steps. When no agents exist, it now shows "Add an agent" instead of "invoke". This aligns TUI behavior with the CLI deploy path (actions.ts) which already handled this correctly.

Related Issue

Closes #507

Documentation PR

N/A

Type of Change

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

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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[jesseturner21]

niceeeee