docs(admin-config-tool): commit spec docs and example configs

design.md, research.md (new), brief.md and requirements.md (updated
during spec authoring: Req 1.6 resolved/superseded by bundling, Req
5.5 added, Req 4.3/4.4 extended for limits.yaml) had been sitting
uncommitted since before implementation began -- the entire 18-task
implementation was built against these documents without them ever
landing in git.

src/configs/*.yaml + schema/*.schema.json: the example config
directory and bundled JSON schemas most of the test suite reads as
"real repo fixtures" (test_config_build.py, test_mapping.py,
test_validation.py, etc.) were likewise never committed -- those
tests would silently skip (skipif guards) rather than run for anyone
else checking out this branch.

src/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