feat(gateway): add read-only gateway commands

[aidandaly24]

Summary

• add read-only gateway get/list, gateway target get/list, and gateway rule get/list commands
• add the Gateway Core client boundary, concrete AWS SDK implementation, router wiring, help defaults, and controllable test client
• add focused handler tests plus recorded AWS fixtures and golden output for successful, paginated, and not-found responses
• document the new Gateway command tree and usage examples

Scope

This PR scaffolds Gateway read handlers only. It does not add Gateway mutations, synchronization, invocation, resource-policy or tag commands, or interactive TUI workflows.

Testing

• bun test (524 passing, 0 failing across 47 files)
• bun test --coverage (95.17% functions, 97.93% lines overall; Gateway implementation files at 100%)
• bun run typecheck
• bun run lint:check
• bun run format:check
• bun run build
• bun run compile (Darwin, Linux, and Windows on x64 and arm64)
• source, bundled dist, native Linux binary, and packed-artifact help smokes for all six commands
• script-free package creation and content audit
• live e2e-test validation for all six reads and second-page token forwarding for Gateway, Target, and Rule lists

The recorded fixture graph uses persistent non-OAuth test resources and contains no credentials or secrets.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.98%. Comparing base (c7f857b) to head (e628edd).

Additional details and impacted files

@@             Coverage Diff              @@
##           refactor    #1869      +/-   ##
============================================
+ Coverage     95.87%   95.98%   +0.11%     
============================================
  Files           198      208      +10     
  Lines          9379     9636     +257     
============================================
+ Hits           8992     9249     +257     
  Misses          387      387              

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[Hweinstock]

lgtm

[Hweinstock]

i really like the test.each pattern, makes for some clear, concise, tests.

[notgitika]

Awesome, LGTM