feat: add root build/test/typecheck scripts (E00-S01-T05)

Adds root scripts so build, test and typecheck run from the workspace root:
- root package.json gains scripts: build (pnpm -r run build), test
  (node --test on tests/**/*.test.mjs), typecheck (pnpm -r run typecheck)
- every workspace package (apps/server, packages/core,
  extensions/example) gains build (tsc -p tsconfig.json) and typecheck
  (tsc -p tsconfig.json --noEmit) scripts
- typescript 6.0.3 pinned as an exact root devDependency so the commands
  run from a clean checkout; lockfile regenerated with pnpm 11.23.0

Verified from a clean state: pnpm install --frozen-lockfile passes,
pnpm build emits dist for all 3 packages, pnpm typecheck passes for all 3,
pnpm test runs tests/architecture-import.test.mjs 10/10 green, and CI's
pnpm -r list --depth -1 still lists all 4 workspace projects.

Closes #158

pnpm-lock.yaml

@@ -6,10 +6,25 @@ settings:
 
 importers:
 
-  .: {}
+  .:
+    devDependencies:
+      typescript:
+        specifier: 6.0.3
+        version: 6.0.3
 
   apps/server: {}
 
   extensions/example: {}
 
   packages/core: {}
+
+packages:
+
+  typescript@6.0.3:
+    resolution: {integrity: sha512-y2TvuxSZPDyQakkFRPZHKFm+KKVqIisdg9/CZwm9ftvKXLP8NRWj38/ODjNbr43SsoXqNuAisEf1GdCxqWcdBw==}
+    engines: {node: '>=14.17'}
+    hasBin: true
+
+snapshots:
+
+  typescript@6.0.3: {}