fix: clear mcp.json gateways during remove-all to prevent orphaned AWS resources

[aidandaly24]

Description

remove -> All only reset agentcore.json, leaving mcp.json untouched. This caused gateway resources (Gateway, Gateway Target, IAM Role) to survive removal — subsequent agentcore deploy saw hasGateways=true, skipped teardown, and kept gateway resources alive in AWS.

This PR adds mcp.json gateway cleanup to both the CLI and TUI remove-all paths:

• handleRemoveAll() (CLI): resets mcp.json gateways after writeProjectSpec()
• useRemoveFlow() (TUI): resets mcp.json gateways in runRemoval() + enumerates gateways/targets in the confirmation list so users see what's being removed

No changes to preflight, teardown, or CDK logic — the existing teardown detection already works correctly once mcp.json is cleared.

Related Issue

Documentation PR

N/A — no user-facing docs changes needed. The behavior now matches what users already expect.

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

Added a new test in remove-all.test.ts that writes mcp.json with a gateway and target, runs remove all --force --json, and verifies agentCoreGateways is cleared to an empty array. All 1892 unit tests pass with 0 failures.

Also manually tested creating a gateway, gateway target, agent. I deployed these resources, then did remove all, and it worked.

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

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the
terms of your choice.