Register qonto-assistant as a protected system (finance.qonto.read)

QONTO-WP-0004-T04. Modeled directly on examples/tenant-engine/: one
resource type (finance-snapshot), one action (finance.qonto.read),
two registered subjects (an agent-harness session identity and the
founder's human identity), and a Rego policy gating on
resource.system + action + subject.type + tenant match. Tenant
capability-role/plan liveness (VEN/CUS) is deliberately NOT encoded
here -- that's qonto-assistant's separate tenant-engine live-lookup
check, per this package's own scope note.

Verified: flex-auth test-policy (6 rego tests + 6 fixtures, all pass),
load-registry, and CLI check for both an allow and a deny case. Also
verified end-to-end over real HTTP: a live flex-auth serve loaded with
this exact registry+policy, hit by qonto-assistant's actual
FlexAuthCheckClient (not a mock) -- allow for tenant:friendly:binky,
deny (wrong_tenant) for a mismatched tenant.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/qonto-assistant/check_request_allow_read.json

@@ -0,0 +1,15 @@
+{
+  "id": "check:qonto-assistant-read-t1",
+  "tenant": "tenant:friendly:binky",
+  "subject": {
+    "id": "agent-harness-binky",
+    "type": "agent"
+  },
+  "action": "finance.qonto.read",
+  "resource": {
+    "id": "finance-snapshot",
+    "type": "finance-snapshot",
+    "system": "qonto-assistant"
+  },
+  "context": {}
+}