feat(cli): add global working directory option

[tbrandenburg]

Summary

• Add one global --cwd <dir> option that validates and changes the CLI process cwd before command actions.
• Preserve path precedence and userDir behavior; reject run --docker --cwd before flow acquisition or Docker work.
• Document working-directory semantics and cover run, inspect, serve, edit, help, and failure paths.

Closes #78

Validation

• make ci — formatting and lint passed; 177 tests passed. Optional audit reported baseline 5 transitive vulnerabilities (2 moderate, 3 high).
• node --test test/integration/edit-acceptance.integration.test.js — 5 passed.
• Manual global-checkout E2E: host run and native serve reported selected project cwd; relative flow and userDir resolution passed; edit list/get/preview/apply passed against a disposable local server; invalid cwd and Docker conflict returned nonzero; server shut down and temporary data was removed.
• Checked a free loopback port before starting the disposable server.

Review and risks

• Adversarial review found no critical/high issues; the medium fixture portability concern was addressed by simplifying Exec commands.
• Permission-denied behavior is handled but was not exercised under a non-privileged test user.
• Optional npm audit remains at baseline: 5 transitive findings (3 high, 2 moderate).