feat(errors): add shared user cancellation error

[aidandaly24]

Problem

Commander exits and user cancellations bypass the shared CLI error model. The root runnable unwraps causes and checks raw error names, while Runtime invoke defines a resource-specific interruption error and rewraps cancellation during response handling.

Solution

• classify CommanderError in AgentCoreCLIError.fromError, preserving help as exit 0 and mapping parse failures to usage exit 2
• add an opt-in SilentCLIError category so only intentionally silent errors skip generic root stderr output
• add a silent, user-sourced UserCancellationError with exit code 130
• use the shared cancellation error as the AbortSignal.reason for Runtime invoke and dataset download SIGINT handling
• preserve Runtime's partial-response interruption summary while propagating the original typed cancellation reason
• leave TUI-local cancellation and low-level platform AbortError handling unchanged

Verification

• bun test src/errors/errors.test.tsx src/runnable/index.test.ts src/handlers/runtime/invoke/response.test.ts src/handlers/runtime/invoke/invoke.test.tsx src/handlers/eval/dataset/dataset.test.tsx (97 pass, 0 fail)
• bun run typecheck
• bun run lint:check
• bun run format:check
• bun run build
• git diff --check
• GitHub full unit suites:
  • Linux: 1110 pass, 0 fail
  • Windows: 1110 pass, 0 fail
  • macOS: 1110 pass, 0 fail
• AgentCore E2E CodeBuild
• bundled CLI smoke checks:
  • root, command-group, and leaf help: exit 0, help on stdout, no stderr or error log
  • nested unknown option: exit 2, one Commander error line, classified as a user error
  • real SIGINT while reading payload stdin: exit 130, no stdout or stderr, structured UserCancellationError log

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.78%. Comparing base (531d068) to head (5e13303).

Additional details and impacted files

@@             Coverage Diff              @@
##           refactor    #1986      +/-   ##
============================================
- Coverage     96.78%   96.78%   -0.01%     
============================================
  Files           326      326              
  Lines         18061    18052       -9     
============================================
- Hits          17480    17471       -9     
  Misses          581      581              

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