test: add unit tests for gateway functionality

[aidandaly24]

Description

Add comprehensive unit test coverage for all MCP Gateway Phase 1 functionality introduced in Batches 1-3 (Tasks 1-9).

86 new test cases across 17 files covering:

• Schema validation: gateway targets, outbound auth, credential discriminated union, deployed state
• OAuth credential provider: full CRUD operations, conflict→update fallback, error paths
• Pre-deploy identity: OAuth setup, credential collection, env var mapping
• CLI validation: existing-endpoint path, credential validation
• Deploy outputs: buildDeployedState with credentials, parseGatewayOutputs
• External target creation: gateway assignment, unassigned targets, duplicate prevention, outboundAuth
• Gateway target removal: listing, preview, removal operations
• Preflight: gateway-only deploy validation
• Credential references: cross-gateway warning on removal
• Add command actions: buildGatewayTargetConfig mapping
• UI: AddScreen/RemoveScreen enablement, ResourceGraph unassigned targets
• Types: constants validation (AUTHORIZER_TYPE_OPTIONS, SKIP_FOR_NOW, SOURCE_OPTIONS)

New test files:

• oauth2-credential-provider.test.ts
• remove-gateway-target.test.ts (operations)
• remove-identity.test.ts
• actions.test.ts (add command)
• AddScreen.test.tsx
• RemoveScreen.test.tsx
• types.test.ts (mcp)

Extended test files:

• mcp.test.ts, agentcore-project.test.ts, deployed-state.test.ts (schemas)
• validate.test.ts, outputs.test.ts, pre-deploy-identity.test.ts, preflight.test.ts
• ResourceGraph.test.tsx, create-mcp.test.ts

Related Issue

Part of the MCP Gateway Phase 1 integration (gateway-integration branch). Task 9c Part 1.

Type of Change

• Other (please describe): Unit test coverage for existing functionality

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

All 1821 tests pass (86 new). Only source change is exporting buildGatewayTargetConfig to enable direct testing.

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