Add settlement links to payment entries for traceability

- Add settled_entry_links parameter to format_payment_entry and format_net_settlement_entry
- Query unsettled expenses/receivables before creating settlement entries
- Pass original entry links to format functions so settlements reference what they settle
- Update all callers in views_api.py (5 locations) and tasks.py (1 location)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

beancount_format.py

@@ -497,7 +497,8 @@ def format_payment_entry(
     fiat_currency: Optional[str] = None,
     fiat_amount: Optional[Decimal] = None,
     payment_hash: Optional[str] = None,
-    reference: Optional[str] = None
+    reference: Optional[str] = None,
+    settled_entry_links: Optional[List[str]] = None
 ) -> Dict[str, Any]:
     """
     Format a payment entry (Lightning payment recorded).
@@ -516,6 +517,7 @@ def format_payment_entry(
         fiat_amount: Optional fiat amount (unsigned)
         payment_hash: Lightning payment hash
         reference: Optional reference
+        settled_entry_links: List of expense/receivable links being settled (e.g., ["exp-abc123"])
 
     Returns:
         Fava API entry dict
@@ -584,6 +586,8 @@ def format_payment_entry(
         entry_meta["payment-hash"] = payment_hash
 
     links = []
+    if settled_entry_links:
+        links.extend(settled_entry_links)
     if reference:
         links.append(reference)
     if payment_hash:
@@ -594,7 +598,7 @@ def format_payment_entry(
         flag="*",  # Cleared (payment already happened)
         narration=description,
         postings=postings,
-        tags=["lightning-payment"],
+        tags=["lightning-payment", "settlement"],
         links=links,
         meta=entry_meta
     )
@@ -713,7 +717,8 @@ def format_net_settlement_entry(
     description: str,
     entry_date: date,
     payment_hash: Optional[str] = None,
-    reference: Optional[str] = None
+    reference: Optional[str] = None,
+    settled_entry_links: Optional[List[str]] = None
 ) -> Dict[str, Any]:
     """
     Format a net settlement payment entry (user paying net balance).
@@ -743,6 +748,7 @@ def format_net_settlement_entry(
         entry_date: Date of payment
         payment_hash: Lightning payment hash
         reference: Optional reference
+        settled_entry_links: List of expense/receivable links being settled (e.g., ["exp-abc123", "rcv-def456"])
 
     Returns:
         Fava API entry dict
@@ -780,6 +786,8 @@ def format_net_settlement_entry(
         entry_meta["payment-hash"] = payment_hash
 
     links = []
+    if settled_entry_links:
+        links.extend(settled_entry_links)
     if reference:
         links.append(reference)
     if payment_hash: