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/milestone-lock.cts

@@ -17,7 +17,7 @@
  * - `.planning/milestone.lock` (workstream-scoped via planningDir) holds
  *   `{ phase, session, pid, updated_at }`.
  * - Session identity reuses `getWorkstreamSessionKey()`
- *   (active-workstream-store.cjs): env-first (GSD_SESSION_KEY,
+ *   (active-workstream-store.cjs): env-first (MSD_SESSION_KEY,
  *   CLAUDE_SESSION_ID, CODEX_THREAD_ID, …), then the controlling TTY. Two
  *   agent sessions in different terminals/runtimes resolve different keys;
  *   headless runs resolve to null.
@@ -136,7 +136,7 @@ function writeClaim(cwd: string, claim: MilestoneClaim): void {
 }
 
 // planningWorkspace.planningDir targets .planning (or the workstream-scoped
-// variant); the parent is created by every GSD command that gets this far, but
+// variant); the parent is created by every MSD command that gets this far, but
 // the claim write must not throw if it is somehow missing.
 function ensureClaimDir(cwd: string): void {
   try {
@@ -171,7 +171,7 @@ export function warnMilestoneConflict(conflict: MilestoneConflict, action: strin
   const holder = conflict.locked_session ?? 'an unknown (headless) session';
   const actor = conflict.session ?? 'an unknown (headless) session';
   process.stderr.write(
-    `[gsd-tools] WARNING: milestone lock conflict (#3311): ${holder} holds the milestone claim for phase ` +
+    `[msd-tools] WARNING: milestone lock conflict (#3311): ${holder} holds the milestone claim for phase ` +
       `${conflict.locked_phase}, but ${actor} is running ${action} for phase ${conflict.phase}. ` +
       `STATE.md's ## Current Position is a single slot — concurrent phases overwrite each other's ` +
       `position. Verify Current Position before trusting it.\n`,