docs: update, polish, and finalize documentation for release

The codebase is evolving significantly. The documentation needs multiple large and small passes to catch up, polish existing content, update pages that carry stale information, and finalize for the release.

Scope

Audit every doc page against the current CLI surface and update commands, flags, and output examples that have drifted
Update reference/cli.md to reflect the renamed CLI commands
Fill in about/release-notes.md (currently 13 lines) with shipped features or link to GitHub Releases
Polish prose across all pages: fix passive voice, tighten wording, ensure consistent terminology (OpenShell vs NemoClaw usage), and verify all cross-page links resolve
Run a full docs build and resolve all warnings and broken references

Approach

Work page-by-page. Each PR should be scoped to one section or a small group of related pages.

Definition of Done

Every doc page reflects the current codebase behavior (CLI flags, policy schema, provider types, sandbox workflows)
No broken cross-references or build warnings
Consistent product naming (OpenShell) and terminology throughout
Release notes page is populated or redirects to GitHub Releases
Architecture content has a single source of truth with clear cross-links