fix(ci): restore cron triggers via per-row cron name filter

The matrix consolidation routed cron events through
`evaluate: 'CI_PIPELINE_CRON == "..."'`, but CI_PIPELINE_CRON is not
exposed to the when.evaluate constraint context, so no matrix row ever
matched and the scheduled process-updates / weekly runs stopped firing.
Switch back to the first-class `cron:` name filter (still parameterized
per matrix row) which the server matches directly against the fired cron.

.crow/weekly-rebuild-missing.yaml

@@ -2,7 +2,7 @@
 # One matrix row per OS/arch replaces the former per-platform files.
 # Routing is preserved 1:1:
 #   - cron:   each existing `weekly-rebuild-missing-<os>-<arch>` cron fires only
-#             its matching matrix row (via CI_PIPELINE_CRON).
+#             its matching matrix row (via the per-row `cron:` name filter).
 #   - manual: `weekly_rebuild_missing` dropdown, default "all" (matches the
 #             previous bare manual trigger that ran every os/arch); pick a
 #             single <os>-<arch> to run just one.
@@ -30,7 +30,7 @@ variables:
 
 when:
   - event: cron
-    evaluate: 'CI_PIPELINE_CRON == "weekly-rebuild-missing-${OS}-${ARCH}"'
+    cron: weekly-rebuild-missing-${OS}-${ARCH}
   - event: manual
     evaluate: 'weekly_rebuild_missing == "all" || weekly_rebuild_missing == "${OS}-${ARCH}"'