feat(dialyzer): add typecheck stage to full CI pipelines

Justfile

@@ -31,6 +31,21 @@ start-database:
 
 ci-dev: lint audit test-fast
 
+# Build the Dialyzer PLT. Idempotent — no-op once the PLT is up to date.
+# First build takes 5–15 min; subsequent runs are seconds. PLT files live in
+# priv/plts/ and are gitignored.
+plt: install-dependencies
+    @mkdir -p priv/plts
+    mix dialyzer --plt
+
+# Typecheck via Dialyzer. Slow stage, NOT part of ci-dev.
+typecheck: plt
+    mix dialyzer --format short
+
+# Full CI: inner loop plus typecheck. Use locally before pushing; Drone CI
+# runs equivalent steps with PLT caching.
+ci: ci-dev typecheck
+
 gettext:
   mix gettext.extract
   mix gettext.merge priv/gettext --on-obsolete=mark_as_obsolete