viewer: drop parties' bill arms (the ledger tags bill entries with their vendor, which wins); burn tests for one covered month and breaking even

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

crates/ledger-gui/src/books.rs

@@ -489,18 +489,15 @@ impl Books {
     }
 }
 
-/// Customer or vendor names for entries created by invoices and bills and
-/// their payments, from the journal.
+/// Customer names for entries created by invoices and their payments,
+/// from the journal. (Bills and bill payments need nothing here: the
+/// ledger tags their entries with the vendor, which takes precedence.)
 fn parties(ledger: &Ledger, journal: &[JournalLine]) -> HashMap<EntryId, String> {
     let mut out = HashMap::new();
     let customer = |id: Option<u64>| {
         id.and_then(|c| ledger.get_customer(c))
             .map(|c| c.name.clone())
     };
-    let vendor = |id: Option<u64>| {
-        id.and_then(|v| ledger.get_vendor(v))
-            .map(|v| v.name.clone())
-    };
     let u = |p: &Value, k: &str| p.get(k).and_then(|v| v.as_u64());
     for line in journal {
         let p = &line.payload;
@@ -514,12 +511,6 @@ fn parties(ledger: &Ledger, journal: &[JournalLine]) -> HashMap<EntryId, String>
                     .and_then(|i| ledger.get_invoice(i))
                     .map(|i| i.customer_id),
             ),
-            "bill.created" => vendor(u(p, "vendor_id")),
-            "bill.paid" => vendor(
-                u(p, "bill_id")
-                    .and_then(|b| ledger.get_bill(b))
-                    .map(|b| b.vendor_id),
-            ),
             _ => None,
         };
         if let Some(n) = name {