refactor: hard-fork GSD -> MSD (Make Software Done)

Mechanical rename produced by scripts/msd-rename.cjs: gsd/Gsd/GSD -> msd/Msd/MSD
across contents and paths, upstream package/repo coordinates -> @golem15/msd-core
and golem15com/msd-core. Deep links into upstream history, sibling upstream
packages, the GSD-2 import feature, CHANGELOG.md and .changeset/ are kept as-is.

Hand edits on top: MSD block-letter banner and logos, LICENSE copyright line,
package/plugin identity, regenerated lockfile, install-tree fixtures, derived
registries and benchmark baseline; migration checksum baseline re-locked
(MSD keeps its own install state, so no install had applied the old sums);
sort-order and regex-escaped expectations in tests adjusted.

src/markdown-sectionizer.cts

@@ -7,7 +7,7 @@
  *
  * ADR-1372 — T0 foundational seam. Migration tiers T1–T7 progressively adopt this seam.
  *
- * ADR-457 build-at-publish: compiled by tsc to gsd-core/bin/lib/markdown-sectionizer.cjs.
+ * ADR-457 build-at-publish: compiled by tsc to msd-core/bin/lib/markdown-sectionizer.cjs.
  */
 
 import { escapeRegex } from './pattern.cjs';
@@ -1127,5 +1127,5 @@ export function deleteSection(
   return collapsedBefore + after;
 }
 
-// Consumers: require('../gsd-core/bin/lib/markdown-sectionizer.cjs')
+// Consumers: require('../msd-core/bin/lib/markdown-sectionizer.cjs')
 // Named CJS exports are the canonical surface (ADR-457 .cts → .cjs build-at-publish).