docs: roll up legacy release notes into a single archive (#658) (#659)

Consolidate all pre-rename release notes (the retired get-shit-done-cc /
get-shit-done-redux lineage, 1.0.0 -> 1.50.0-canary.1) into one condensed,
read-only archive so the legacy 1.x version numbers no longer collide with
the current @opengsd/gsd-core line.

- Add docs/RELEASE-NOTES-LEGACY.md: rename banner, master version-index
  table, condensed per-version sections (1.42.3 -> 1.0.0), and a separate
  pre-release & canary builds section. Stale install commands stripped.
- Trim CHANGELOG.md to the current @opengsd/gsd-core line only; replace the
  Legacy Release History block with a pointer to the archive and drop the
  orphaned numbered legacy reference-link definitions.
- Remove the 10 standalone docs/RELEASE-v*.md files.
- Repoint docs/CANARY.md and docs/FEATURES.md links to the new archive.

Closes #658

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/CANARY.md

@@ -61,6 +61,6 @@ File against the [issue tracker](https://github.com/open-gsd/gsd-core/issues) wi
 
 ## Where to look next
 
-- Active canary release notes: [`docs/RELEASE-v1.50.0-canary.1.md`](RELEASE-v1.50.0-canary.1.md)
+- Active canary release notes: [`v1.50.0-canary.1` (now in the legacy release-notes archive)](RELEASE-NOTES-LEGACY.md)
 - Stable release notes: [`CHANGELOG.md`](../CHANGELOG.md)
 - Stream architecture rationale: discussed across [#2727](https://github.com/open-gsd/gsd-core/issues/2727), [#2773](https://github.com/open-gsd/gsd-core/issues/2773) (codex schema-break and the resulting promotion bottleneck that motivated explicit stream isolation)