change main docs structuring

[crowlKats]

[lunadogbot]

1. sidebarUrlMap[normalizedUrl] only does an exact lookup, and runtime/_data.ts now keeps Standard Library as a single /runtime/reference/std/ entry. Existing nested std pages such as /runtime/reference/std/assert/ are no longer mapped to the package sidebar, so they fall back to basicsSidebar. Please add prefix routing for this tree or keep/generated-map the std module hrefs.
2. reference_gen/parallel-doc.ts is under the generated reference tree. Repo rules keep reference/ and reference_gen/ changes upstream-generated, so this formatting fix should come from the generator/upstream source or be split with maintainer confirmation.

[fibibot]

The runtime subnav routing loses nested pages that are not enumerated in sidebarUrlMap, and this also hand-edits generated reference output.

1. sidebarUrlMap[normalizedUrl] only accepts exact URLs, but runtime/_data.ts now keeps std as a single Standard Library entry at /runtime/reference/std/. Pages like /runtime/reference/std/assert/ are not collected, so they fall back to basicsSidebar instead of the package/std sidebar. Add prefix routing for std or keep the child hrefs in the map.
2. reference_gen/parallel-doc.ts is under generated reference output. Repo policy keeps reference/ and reference_gen/ changes generated from upstream sources, so this formatting fix should be split or regenerated instead of hand-edited here.