ci(crewing): also run PR checks for PRs into feat/crewing-foundations

The crewing module is built as a stack of feature-flagged phases that land on
feat/crewing-foundations (the integration branch) before the whole thing merges
to master. PRs into that branch were skipped because pr-checks only triggered on
`branches: [master]`. Add feat/crewing-foundations so each stacked phase PR runs
the same hard gates (test-presence policy, type-check, unit + integration).

For pull_request events the workflow is read from the base branch, so this must
live on feat/crewing-foundations to take effect for PRs targeting it.

.forgejo/workflows/pr-checks.yml

@@ -1,15 +1,20 @@
 name: PR checks
 
-# Enforces the contribution policy on every PR into master (all gates hard):
+# Enforces the contribution policy on every PR into master — plus the crewing
+# integration branch (feat/crewing-foundations), which collects the stacked,
+# feature-flagged crewing phases before they merge to master. Same hard gates:
 #   - code changes must ship with tests (docs/config/automation are exempt)
 #   - type-check is clean across the whole project (tests included)
 #   - unit tests pass
 #   - integration tests pass against an ephemeral Postgres (migrate + seed)
 # Runs on the pms1 host runner. See automation/README.md > "Contribution policy".
+#
+# Note: for pull_request events the workflow is read from the BASE branch, so a
+# base must appear in this list for its incoming PRs to be checked.
 
 on:
   pull_request:
-    branches: [master]
+    branches: [master, feat/crewing-foundations]
 
 jobs:
   checks: