docs: sync documentation for v1.0.0 freeze

Mark LanguageRef as normative, add docs index, update README/Packages/
Stdlib/BuildAndTest status lines, archive PLAN.md and QUALITY_PLAN
pointers to RELEASE_v1.0.0 and active SEMVER.

docs/README.md

@@ -0,0 +1,17 @@
+# Bux documentation index
+
+**Language version:** **v1.0.0** (freeze) — tag `v1.0.0`
+
+| Document | Role |
+|----------|------|
+| [LanguageRef.md](LanguageRef.md) | **Normative** language specification |
+| [Stdlib.md](Stdlib.md) | Standard library overview / API tables |
+| [BuildAndTest.md](BuildAndTest.md) | Build, test, cross, static, containers |
+| [Packages.md](Packages.md) | Manifests, registry, lockfiles |
+| [SEMVER.md](SEMVER.md) | Versioning policy (active after 1.0) |
+| [RELEASE_v1.0.0.md](RELEASE_v1.0.0.md) | v1.0.0 release / freeze notes |
+| [ROADMAP.md](ROADMAP.md) | Language construct checklist |
+| [QUALITY_PLAN.md](QUALITY_PLAN.md) | Session log + path to v1.0 (archive) |
+| [api/stdlib.md](api/stdlib.md) | Generated API docs from `///` (via `make docs`) |
+
+Parent tree: [../README.md](../README.md) · historical plan: [../PLAN.md](../PLAN.md)