fix(campaigns/expiry-picker): show + save dates in America/Montreal TZ

The edit-params picker was showing "2026-06-22" for an expiry stored
as 2026-06-22T03:59:59Z because it sliced the UTC string. But that
UTC instant is actually 23:59 EDT on June 21 in Montreal, which is
what the email recipient sees (and what the operator picked).

Fixes both sides of the round-trip:

DISPLAY (UTC → picker)
- Convert stored ISO UTC to YYYY-MM-DD interpreted in America/Montreal
  using en-CA locale (which returns ISO-style YYYY-MM-DD).

SAVE (picker → ISO UTC)
- New endOfDayMontreal() helper that probes Montreal's offset for the
  target date (noon UTC always lands in morning Montreal, never spans
  a day) and anchors at 23:59:59.999 local. Handles EDT/EST swaps
  automatically — verified with edge cases 2026-03-08 (post-DST-spring),
  2026-06-21 (mid-summer), 2026-11-01 (post-DST-fall), 2026-12-31 (winter).

Previously the save path relied on the BROWSER's local TZ inference
(new Date('YYYY-MM-DDT23:59:59').toISOString()) which is fine for
Quebec operators but quietly wrong for anyone editing from elsewhere.

The bulk email send was already correct because the worker's
toLocaleDateString uses timeZone: 'America/Montreal' (last commit).
This commit only fixes what the OPERATOR sees in the picker.

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

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/ops/src/modules/campaigns/pages/CampaignDetailPage.vue

@@ -253,6 +253,23 @@ function dateAfterToday (dateStr) {
   return d.getTime() > Date.now()
 }
 
+// Convert a YYYY-MM-DD string to the ISO UTC of end-of-day on that date,
+// interpreted as Montreal local. Handles EDT (UTC-4 summer) and EST (UTC-5
+// winter) by probing what hour Intl reports at noon UTC on the same date —
+// noon UTC is always morning in Montreal, so the date never rolls over.
+function endOfDayMontreal (yyyyMmDd) {
+  const [y, m, d] = yyyyMmDd.split('-').map(Number)
+  const probe = new Date(Date.UTC(y, m - 1, d, 12, 0, 0))   // noon UTC on the target date
+  const mtlHour = parseInt(new Intl.DateTimeFormat('en-US', {
+    hour: '2-digit', hour12: false, timeZone: 'America/Montreal',
+  }).format(probe), 10)
+  // Noon UTC reads as 08:00 in EDT or 07:00 in EST → offset = 12 - mtlHour
+  const offsetHours = 12 - mtlHour
+  // End of day Montreal = 23:59:59 Mtl → (23 + offsetHours):59:59 UTC, rolls
+  // over to the next UTC day during summer (EDT).
+  return new Date(Date.UTC(y, m - 1, d, 23 + offsetHours, 59, 59, 999)).toISOString()
+}
+
 // Template lists for the FR/EN dropdowns in the dialog. Refreshed lazily
 // when the dropdown opens so newly-created templates show up without a
 // page reload.
@@ -443,9 +460,15 @@ async function retryFailedRow (row) {
 // dropdowns are populated when the dialog mounts.
 function openEditParams () {
   const p = campaign.value?.params || {}
-  // Convert the stored full ISO datetime back to YYYY-MM-DD for the picker.
+  // Convert the stored UTC datetime back to YYYY-MM-DD as displayed in
+  // America/Montreal — without this, a timestamp stored as 03:59 UTC
+  // (= 23:59 EDT the previous day) shows the WRONG day in the picker
+  // because .toISOString() outputs UTC. en-CA locale gives YYYY-MM-DD.
   const expiresAtDisplay = p.gift_expires_at
-    ? new Date(p.gift_expires_at).toISOString().slice(0, 10)
+    ? new Intl.DateTimeFormat('en-CA', {
+        year: 'numeric', month: '2-digit', day: '2-digit',
+        timeZone: 'America/Montreal',
+      }).format(new Date(p.gift_expires_at))
     : ''
   editParams.value = {
     name:              campaign.value?.name || '',
@@ -469,11 +492,13 @@ async function saveEditParams () {
   savingParams.value = true
   try {
     // Translate the YYYY-MM-DD picker value into the full ISO datetime the
-    // hub stores. Anchor at end-of-day local so "until June 15" stays valid
-    // through all of June 15. Empty → fall back to gift_expiry_days on the
-    // hub side. PATCH merges into params, so explicitly send null to clear.
+    // hub stores. Anchor at end-of-day America/Montreal so "until June 21"
+    // stays valid through all of June 21 Quebec time, regardless of where
+    // the operator's browser is set. Empty → fall back to gift_expiry_days
+    // on the hub side. PATCH merges into params, so explicitly send null
+    // to clear.
     const giftExpiresAt = editParams.value.gift_expires_at_display
-      ? new Date(editParams.value.gift_expires_at_display + 'T23:59:59').toISOString()
+      ? endOfDayMontreal(editParams.value.gift_expires_at_display)
       : null
     await updateCampaign(id, {
       name: editParams.value.name,

apps/ops/src/modules/campaigns/pages/CampaignNewPage.vue

@@ -642,6 +642,17 @@ function dateAfterToday (date) {
   d.setHours(23, 59, 59, 999)
   return d.getTime() > Date.now()
 }
+// Mirror of CampaignDetailPage's helper — see that file for the algorithm.
+// Anchors at end-of-day America/Montreal regardless of the operator's TZ.
+function endOfDayMontreal (yyyyMmDd) {
+  const [y, m, d] = yyyyMmDd.split('-').map(Number)
+  const probe = new Date(Date.UTC(y, m - 1, d, 12, 0, 0))
+  const mtlHour = parseInt(new Intl.DateTimeFormat('en-US', {
+    hour: '2-digit', hour12: false, timeZone: 'America/Montreal',
+  }).format(probe), 10)
+  const offsetHours = 12 - mtlHour
+  return new Date(Date.UTC(y, m - 1, d, 23 + offsetHours, 59, 59, 999)).toISOString()
+}
 const daysUntilExplicitDate = computed(() => {
   if (!params.value.gift_expires_at_display) return 0
   const target = new Date(params.value.gift_expires_at_display + 'T23:59:59')
@@ -1082,7 +1093,8 @@ async function launchSend () {
     // local time so "until June 15" really means through all of June 15.
     const apiParams = { ...params.value }
     if (apiParams.gift_expires_at_display) {
-      apiParams.gift_expires_at = new Date(apiParams.gift_expires_at_display + 'T23:59:59').toISOString()
+      // Anchor at 23:59:59 America/Montreal — handles EDT/EST automatically.
+      apiParams.gift_expires_at = endOfDayMontreal(apiParams.gift_expires_at_display)
     } else {
       delete apiParams.gift_expires_at
     }