feat(gateway): add create commands

[aidandaly24]

Summary

• add Gateway, Target, and Rule create commands
• create a deterministic, tagged, least-privilege Gateway execution role when --role-arn is omitted
• reconcile Target-specific permissions before Target creation and roll them back when creation fails
• preserve customer-managed roles without IAM mutation
• limit the command surface to fields modeled by @aws-sdk/client-bedrock-agentcore-control@3.1102.0

Stack

• base: refactor
• this PR: feat(gateway): add create commands #1899
• next: feat(gateway): add update commands #1900
• top: feat(gateway): add delete commands #1901

Testing

• bun test src/core/gatewayExecutionRole.test.ts src/core/gateway.create.test.ts src/handlers/gateway/gateway.create.test.tsx src/handlers/gateway/gateway.test.tsx (52 pass)
• source-scoped TypeScript, lint, and formatting checks
• live AWS test with AWS_PROFILE=deploy: auto-created Gateway role, failed Target-create policy rollback, and successful Lambda Target policy creation

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.83037% with 64 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.85%. Comparing base (a08c73f) to head (bb5a72d).
⚠️ Report is 4 commits behind head on refactor.

Files with missing lines	Patch %	Lines
src/core/gatewayExecutionRole.ts	95.93%	28 Missing ⚠️
src/handlers/gateway/mutations.ts	76.25%	19 Missing ⚠️
src/handlers/gateway/create/index.tsx	91.52%	10 Missing ⚠️
src/handlers/gateway/target/create/index.tsx	94.94%	5 Missing ⚠️
src/handlers/gateway/rule/create/index.tsx	95.55%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           refactor    #1899      +/-   ##
============================================
- Coverage     95.98%   95.85%   -0.14%     
============================================
  Files           208      213       +5     
  Lines          9636    10873    +1237     
============================================
+ Hits           9249    10422    +1173     
- Misses          387      451      +64     

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