build(test): collapse the typecheck to a single program

The src-only tsc pass was redundant with the tests pass: tsconfig.tests.json
extends the base config, so its program loads every src file (96/96, both
passes identical) plus the specs, and tsc type-checks the whole program —
injected src errors surface from the tests pass alone. Verified zero src-only
diagnostics on the clean tree. One pass now covers src + tests; drop the
duplicated full-program compile.

package.json

@@ -44,7 +44,7 @@
     "watch": "bash scripts/watch.sh",
     "web": "bash scripts/web.sh",
     "register": "bash scripts/register.sh",
-    "typecheck": "tsc --noEmit & tsc --noEmit -p tsconfig.tests.json & wait",
+    "typecheck": "tsc --noEmit -p tsconfig.tests.json",
     "test": "pnpm run typecheck && vitest run --coverage",
     "coverage": "vitest run --coverage",
     "release": "bash scripts/publish.sh",