Split boundary.sx: separate language contract from app-specific declarations

boundary.sx was mixing three concerns in one file:
- Core SX I/O primitives (the language contract)
- Deployment-specific layout I/O (app architecture)
- Per-service page helpers (fully app-specific)

Now split into three tiers:
1. shared/sx/ref/boundary.sx — core I/O only (frag, query, current-user, etc.)
2. shared/sx/ref/boundary-app.sx — deployment layout contexts (*-header-ctx, *-ctx)
3. {service}/sx/boundary.sx — per-service page helpers

The boundary parser loads all three tiers automatically. Validation error
messages now point to the correct file for each tier.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

events/sx/boundary.sx

@@ -0,0 +1,61 @@
+;; Events service — page helper declarations.
+
+(define-page-helper "calendar-admin-data"
+  :params (&key calendar-slug)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "day-admin-data"
+  :params (&key calendar-slug year month day)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "slots-data"
+  :params (&key calendar-slug)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "slot-data"
+  :params (&key calendar-slug slot-id)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "entry-data"
+  :params (&key calendar-slug entry-id)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "entry-admin-data"
+  :params (&key calendar-slug entry-id year month day)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "ticket-types-data"
+  :params (&key calendar-slug entry-id year month day)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "ticket-type-data"
+  :params (&key calendar-slug entry-id ticket-type-id year month day)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "tickets-data"
+  :params (&key)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "ticket-detail-data"
+  :params (&key code)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "ticket-admin-data"
+  :params (&key)
+  :returns "dict"
+  :service "events")
+
+(define-page-helper "markets-data"
+  :params (&key)
+  :returns "dict"
+  :service "events")