feat: add auth token command

[jlitola]

Summary

• add githits auth token to print the current bearer token to stdout
• respect GITHITS_API_TOKEN before local storage and GITHITS_MCP_URL for auth environment selection
• refresh expired stored OAuth tokens and fail non-zero when unauthenticated

Review

• code reviewer: no findings
• residual note: no full CLI-level stdout/stderr integration test; action-level stdout behavior and auto-login exemption are covered

Tests

• bun test src/commands/auth-status.test.ts
• bun test src/shared/auto-login.test.ts
• bun test src/cli.test.ts
• bun test src/commands/auth-json.test.ts
• bun test src/shared/command-metadata.test.ts
• bun run typecheck
• bun run build
• bun run ./src/cli.ts auth token --help

Notes

• did not run githits auth token against real credentials to avoid exposing a live token