feat: teach AI classifier to recognize "comp" and tooth surface notation

Add "comp" as alias for composite in CDT lookup. Update classifier
prompt with explicit examples for "claim comp #8 ml for lisa today"
and dental surface letter definitions (M/D/L/F/B/O/V/I) so the LLM
correctly treats #tooth+surfaces as composite fillings, not insurance.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/Backend/src/routes/payments-reports.ts

@@ -87,6 +87,51 @@ router.get(
   }
 );
 
+/**
+ * GET /api/payments-reports/patients-with-zero-balances
+ * Returns patients fully paid (balance <= 0) within the date/provider filter.
+ */
+router.get(
+  "/patients-with-zero-balances",
+  async (req: Request, res: Response): Promise<any> => {
+    try {
+      const limit = Math.max(
+        1,
+        Math.min(200, parseInt(String(req.query.limit || "25"), 10))
+      );
+      const cursor =
+        typeof req.query.cursor === "string" ? String(req.query.cursor) : null;
+      const from = req.query.from ? new Date(String(req.query.from)) : undefined;
+      const to = req.query.to ? new Date(String(req.query.to)) : undefined;
+
+      if (req.query.from && isNaN(from?.getTime() ?? NaN))
+        return res.status(400).json({ message: "Invalid 'from' date" });
+      if (req.query.to && isNaN(to?.getTime() ?? NaN))
+        return res.status(400).json({ message: "Invalid 'to' date" });
+
+      const npiProviderId = req.query.npiProviderId
+        ? Number(req.query.npiProviderId)
+        : null;
+
+      const data = await storage.getPatientsWithZeroBalance(
+        limit,
+        cursor,
+        from,
+        to,
+        npiProviderId
+      );
+      res.json(data);
+    } catch (err: any) {
+      console.error(
+        "GET /api/payments-reports/patients-with-zero-balances error:",
+        err?.message ?? err,
+        err?.stack
+      );
+      res.status(500).json({ message: "Failed to fetch zero-balance patients" });
+    }
+  }
+);
+
 /**
  * GET /api/payments-reports/by-doctor/balances
  * Query params: