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.

docs/features/workstream-namespacing.md

@@ -4,7 +4,7 @@ title: Workstream Namespacing
 group: v1.28 Features
 ---
 
-**Command:** `/gsd-workstreams`
+**Command:** `/msd-workstreams`
 
 **Purpose:** Parallel workstreams for concurrent work on different milestone areas.
 
@@ -20,5 +20,5 @@ group: v1.28 Features
 
 **Process:**
 1. **Create** — Initialize a named workstream with isolated `.planning/workstreams/{name}/` directory
-2. **Switch** — Change active workstream context for subsequent GSD commands
+2. **Switch** — Change active workstream context for subsequent MSD commands
 3. **Manage** — List, check status, track progress, complete, or resume workstreams