fix: unify tender countdowns and add monthly calendar navigation

src/services/tenderCalendar.js

@@ -36,3 +36,32 @@ export function createTenderICS(t, now = new Date()) {
     `DESCRIPTION:${escapeICS('İKN: '+t.ikn+' — '+t.kurum)}`,
     'END:VEVENT','END:VCALENDAR',''].map(fold).join('\r\n');
 }
+
+export const istanbulDateKey = (now = new Date()) => new Date(now.getTime() + 3 * 3600000).toISOString().slice(0,10);
+export function tenderDateKey(t) {
+  const m = /^(\d{2})\.(\d{2})\.(\d{4})(?:$|\s)/.exec(String(t?.tarih || ''));
+  if (!m) return null;
+  const key = `${m[3]}-${m[2]}-${m[1]}`;
+  const date = new Date(key + 'T00:00:00Z');
+  return !Number.isNaN(date.getTime()) && date.toISOString().slice(0,10) === key ? key : null;
+}
+export function deadlineInfo(t, now = new Date()) {
+  const dateKey = tenderDateKey(t);
+  if (!dateKey) return {dateKey:null,days:null,expired:null,label:'Tarih doğrulanmalı',deadline:null};
+  const days = Math.round((Date.parse(dateKey+'T00:00:00Z') - Date.parse(istanbulDateKey(now)+'T00:00:00Z')) / 86400000);
+  let deadline = null;
+  try { deadline = tenderDeadline(t); } catch { /* an unknown time is not midnight */ }
+  const expired = deadline ? deadline.getTime() <= now.getTime() : days < 0 ? true : null;
+  const label = expired ? 'Süresi geçti' : `${days === 0 ? 'BUGÜN' : days + ' gün'}${deadline ? '' : ' · saat doğrulanmalı'}`;
+  return {dateKey,days,expired,label,deadline};
+}
+export function calendarMonthDays(month) {
+  if (!/^\d{4}-(0[1-9]|1[0-2])$/.test(month)) return [];
+  const [year,m] = month.split('-').map(Number);
+  const count = new Date(Date.UTC(year,m,0)).getUTCDate();
+  return Array.from({length:count},(_,i)=>{
+    const day=String(i+1).padStart(2,'0');
+    return {key:`${month}-${day}`,date:`${day}.${String(m).padStart(2,'0')}.${year}`,
+      label:new Date(`${month}-${day}T12:00:00Z`).toLocaleDateString('tr-TR',{weekday:'short',timeZone:'Europe/Istanbul'})};
+  });
+}