feat(admin-config-tool): task 5.4 - golden-file build determinism tests

tests/fixtures/{minimal,full}/configs/*.yaml + checked-in expected.bin
golden files, added to test_config_build.py. Catches representation
drift (bytes changing even when decoded content stays correct) that
the existing structural/decode-based assertions can't detect.

src/xceadmin/tests/fixtures/full/configs/limits.yaml

@@ -0,0 +1,49 @@
+---
+limits:
+    # cap total slots for ug1 across the whole cluster
+  - name: ug1_slots
+    users:
+      members:
+        - ug1
+    resname: slots
+    value: 10
+
+    # per-user slot cap inside ug2 (each member gets up to 4, not a shared pool)
+  - name: ug2_slots_per_user
+    users:
+      members:
+        - ug2
+      exclude_members:
+        - user3
+    resname: slots
+    value: 4
+    per_user: true
+
+    # queue-scoped memory cap, percentage of total mem resource
+  - name: night_mem_pct
+    queues:
+      members:
+        - night
+    resname: mem
+    value: 50
+    percent: true
+
+    # host-scoped cap, applied per host in hg1
+  - name: hg1_slots_per_host
+    hosts:
+      members:
+        - hg1
+    resname: slots
+    value: 20
+    per_host: true
+
+    # combined scope: ug1 members on the normal queue
+  - name: ug1_normal_slots
+    users:
+      members:
+        - ug1
+    queues:
+      members:
+        - normal
+    resname: slots
+    value: 8