fix(onboarding): add one-command Codex setup and preserve user guides

[HeftyKoo]

Summary

Keep the existing product introduction, Chill/Focus/Watch modes, demo and tutorial videos, browser store links, DSH setup and authorization steps, and everyday controls in both READMEs. Add a focused Codex section with one-command terminal setup and session notifications. Remove internal release-readiness notes from user documentation and keep source-build instructions in the development guide.

The installer supports curl ... | bash, uses a user-owned npm prefix, configures the terminal service, Chrome pairing and Codex integration, and adds the management command to the login-shell PATH without changing npm's global configuration. Update installation, support and privacy documents to match.

Fix the shutdown integration test to observe the unfinished HTTP connection closing. Linux may reset that connection during closeAllConnections; the test permits only that expected error and still verifies clean host exit and lock cleanup.

Validation

• Local pnpm release:audit passed: 202 tests passed / 1 opt-in DSH test skipped, all browser builds, native Safari validation, reproducible packages and an isolated real-shell round trip.
• Installer tests cover piped Bash input, paths with spaces, repeat setup, preserving shell configuration, package/setup failures, unsupported platforms/root/old Node and truncated input.
• Actual packaged global installation into a temporary user prefix with spaces passed.
• Markdown local links and staged diff checks passed.
• GitHub Actions passed both the complete release audit and latest DSH compatibility checks on f3c7c0327d52b40a6b8c347ba50be7dc5c60a0c0: https://github.com/HeftyKoo/AgentOnWeb/actions/runs/36516671745.

The public installation path requires merging the installer and publishing the 0.2.0 npm package and matching store extension. This PR does not publish those releases.

Awaiting maintainer review. Do not merge or enable auto-merge.