fix(spec): bump PROTOCOL_VERSION 12.0.0 → 13.0.0 to match spec major (lockstep)

The version-packages roll (#2720) took @objectstack/spec to major 13.0.0 but
left PROTOCOL_VERSION at 12.0.0, so protocol-version.test.ts — the lockstep
guard asserting the protocol major equals the package major — failed on main,
reddening Test Core for every open PR. Restore the lockstep so the
loader/installer handshake advertises the major the package actually ships.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: os-zhuang

.changeset/protocol-version-13-lockstep.md

@@ -0,0 +1,11 @@
+---
+'@objectstack/spec': patch
+---
+
+fix(spec): bump PROTOCOL_VERSION 12.0.0 → 13.0.0 to match the spec major
+
+The version-packages roll (#2720) took `@objectstack/spec` to major `13.0.0`
+but left `PROTOCOL_VERSION` at `12.0.0`, so `protocol-version.test.ts` (the
+lockstep guard that asserts the protocol major equals the package major) failed
+on `main` — reddening Test Core for every PR. Restore the lockstep so the
+loader/installer handshake advertises the major the package actually ships.

packages/spec/src/kernel/protocol-version.ts

@@ -15,7 +15,7 @@
  * Kept in lockstep with the package's own major; `protocol-version.test.ts`
  * asserts it against `package.json` so the two cannot drift.
  */
-export const PROTOCOL_VERSION = '12.0.0';
+export const PROTOCOL_VERSION = '13.0.0';
 
 /** The protocol major as an integer — the value the handshake compares. */
 export const PROTOCOL_MAJOR: number = Number.parseInt(PROTOCOL_VERSION.split('.')[0]!, 10);