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/FEATURES.md

@@ -2817,7 +2817,7 @@ Source commit: abc1234 (3 commits behind HEAD)
 - REQ-PKG-GATE-02: Planner MUST gate unverified or suspicious package installs before execution.
 - REQ-PKG-GATE-03: Executor MUST NOT auto-substitute package names after failed package-manager installs.
 
-**Reference:** [v1.42.1 Release Notes](RELEASE-v1.42.1.md)
+**Reference:** [v1.42.1 Release Notes](RELEASE-NOTES-LEGACY.md)
 
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