Initial InfraPulse scaffold

docs/plugin-design.md

@@ -0,0 +1,36 @@
+# Plugin Design
+
+Plugins will let InfraPulse add collectors and discovery logic without hard-coding every integration into the core API.
+
+Target shape:
+
+```python
+class InfraPulsePlugin:
+    name: str
+    display_name: str
+
+    def test_connection(self, target, credentials):
+        pass
+
+    def discover(self, target, credentials):
+        pass
+
+    def collect(self, monitor):
+        pass
+
+    def default_alert_rules(self, discovered_item):
+        pass
+```
+
+The first implementation can use simple internal collectors, but the interfaces should preserve this path.
+
+Planned plugin areas:
+
+- Website checks
+- Generic SNMP
+- Proxmox VE
+- Docker
+- UniFi
+- TrueNAS
+- Technitium DNS
+- Active Directory