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.

capabilities/antigravity/capability.json

@@ -7,7 +7,7 @@
   "tier": "core",
   "requires": [],
   "engines": {
-    "gsd": ">=1.6.0"
+    "msd": ">=1.6.0"
   },
   "runtime": {
     "configHome": {
@@ -22,7 +22,7 @@
         "antigravity-ide",
         "antigravity-cli"
       ],
-      "probeExists": "gsd-core/VERSION"
+      "probeExists": "msd-core/VERSION"
     },
     "localConfigDir": ".agents",
     "configFormat": "settings-json",
@@ -31,7 +31,7 @@
         {
           "kind": "skills",
           "destSubpath": "skills",
-          "prefix": "gsd-",
+          "prefix": "msd-",
           "nesting": "flat",
           "recursive": false,
           "converter": "convertClaudeCommandToAntigravitySkill",
@@ -40,7 +40,7 @@
         {
           "kind": "agents",
           "destSubpath": "agents",
-          "prefix": "gsd-",
+          "prefix": "msd-",
           "nesting": "flat",
           "recursive": false,
           "converter": "convertClaudeAgentToAntigravityAgent",
@@ -51,7 +51,7 @@
         {
           "kind": "skills",
           "destSubpath": "skills",
-          "prefix": "gsd-",
+          "prefix": "msd-",
           "nesting": "flat",
           "recursive": false,
           "converter": "convertClaudeCommandToAntigravitySkill"
@@ -59,7 +59,7 @@
         {
           "kind": "agents",
           "destSubpath": "agents",
-          "prefix": "gsd-",
+          "prefix": "msd-",
           "nesting": "flat",
           "recursive": false,
           "converter": "convertClaudeAgentToAntigravityAgent"