feat(traces): add JSON output

[notgitika]

Summary

• add --json to traces list and traces get
• serialize successful results and failures without Ink output in JSON mode
• preserve existing human-readable rendering when the flag is omitted
• document the new options and add command-level regression coverage

Fixes #624

Testing

• npx vitest run --project unit src/cli/commands/traces src/cli/operations/traces (24 tests passed)
• npm run typecheck
• npx eslint src/cli/commands/traces/command.tsx src/cli/commands/traces/types.ts src/cli/commands/traces/__tests__/command.test.ts
• npx prettier --check docs/commands.md src/cli/commands/traces/command.tsx src/cli/commands/traces/types.ts src/cli/commands/traces/__tests__/command.test.ts
• npm run build
• packaged CLI smoke tests: traces list --json and traces get trace-1 --json emit one JSON error object and exit 1 outside a project

[agentcore-devx-automation]

Claude Security Review: no high-confidence findings. (run)

[github-actions]

Package Tarball

aws-agentcore-0.24.1.tgz

How to install

gh release download pr-1782-tarball --repo aws/agentcore-cli --pattern "*.tgz" --dir /tmp/pr-tarball
npm install -g /tmp/pr-tarball/aws-agentcore-0.24.1.tgz

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	39.98%	14848 / 37132
🔵	Statements	39.24%	15822 / 40319
🔵	Functions	34.02%	2526 / 7424
🔵	Branches	33.45%	9884 / 29545

Generated in workflow #4132 for commit ea92553 by the Vitest Coverage Report Action