Per-recipient project codes

Each charge-to entry in config.yml can now have its own project-codes
list. Selecting a recipient swaps the project code dropdown to that
recipient's codes; switching back to Select or Other restores the
global list. Falls back to the global list if a recipient has no
project-codes defined.

app/config.yml

@@ -119,6 +119,10 @@ charge-to:
     vat-id: "US-EIN-12-3456789"
     reg-no: ""
     currency: USD
+    project-codes:
+      - AC-100
+      - AC-110
+      - AC-200
   - display: Example NGO
     name: Example Non-Profit Organisation
     address1: 45 Charity Lane
@@ -131,6 +135,10 @@ charge-to:
     vat-id: "GB123456789"
     reg-no: "01234567"
     currency: GBP
+    project-codes:
+      - NGO-2026-01
+      - NGO-2026-02
+      - NGO-2026-03
 
 # ── Project codes ──────────────────────────────────────────────────────────────
 project-codes:

app/index.html

@@ -693,6 +693,20 @@ function buildForm() {
   calcPayBy();  // compute initial pay-by from default 7-day term
 }
 
+// ── Project-code dropdown ─────────────────────────────────────────────────────
+function updateProjectCodes(codes) {
+  const arr = (codes && codes.length) ? codes : (cfg["project-codes"] || []);
+  const sel = document.getElementById("pcode");
+  if (!sel) return;
+  const prev = sel.value;
+  sel.innerHTML = `<option value="">${t("select")}</option>`
+    + arr.map(pc => `<option value="${h(pc)}">${h(pc)}</option>`).join("")
+    + `<option value="__other__">${t("other")}</option>`;
+  sel.value = arr.includes(prev) ? prev : "";
+  const wrap = document.getElementById("pcode-other-wrap");
+  if (wrap) wrap.style.display = sel.value === "__other__" ? "block" : "none";
+}
+
 // ── Fill charge-to ────────────────────────────────────────────────────────────
 function fillChargeTo(v) {
   const f      = (id, val) => { const el = document.getElementById(id); if (el) el.value = val ?? ""; };
@@ -704,10 +718,12 @@ function fillChargeTo(v) {
   if (v === "") {
     ["ctn","ca1","ca2","ca3","ca4","cc","cph","cem","cvat","creg"].forEach(id => f(id, ""));
     fields?.classList.add("locked");
+    updateProjectCodes(null);   // restore global project codes
     return;
   }
   if (v === "__other__") {
     fields?.classList.remove("locked");
+    updateProjectCodes(null);   // restore global project codes
     return;
   }
   const ct = (cfg["charge-to"] || [])[+v];
@@ -719,6 +735,9 @@ function fillChargeTo(v) {
   f("cvat", ct["vat-id"]);  f("creg", ct["reg-no"]);
   fields?.classList.add("locked");
 
+  // Swap project codes to this recipient's list (falls back to global if none defined)
+  updateProjectCodes(ct["project-codes"] || null);
+
   // Auto-set invoice currency from recipient config
   if (ct.currency) {
     const icurEl = document.getElementById("icur");