feat(psa): implement list_members in ConnectWise provider with cache

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/services/psa/connectwise/provider.py

@@ -231,7 +231,33 @@ class ConnectWiseProvider(PSAProvider):
         return self._map_ticket(data)
 
     async def list_members(self) -> list[PSAMember]:
-        raise NotImplementedError("Implemented in Slice 5")
+        """List CW system members (cached 15 minutes)."""
+        cache_key = "members:all"
+        cached = psa_cache.get(cache_key)
+        if cached is not None:
+            return cached
+
+        data = await self.client.get_paginated(
+            "/system/members",
+            params={
+                "fields": "id,identifier,firstName,lastName,officeEmail",
+                "conditions": "inactiveFlag = false",
+                "pageSize": 1000,
+            },
+        )
+
+        result = [
+            PSAMember(
+                id=str(m["id"]),
+                identifier=m.get("identifier", ""),
+                name=f"{m.get('firstName', '')} {m.get('lastName', '')}".strip(),
+                email=m.get("officeEmail"),
+            )
+            for m in data
+        ]
+
+        psa_cache.set(cache_key, result, ttl_seconds=900)
+        return result
 
     # ── Private helpers ───────────────────────────────────────────────