Format timestamps as Asia/Dushanbe (UTC+5)

SQLite stores all timestamps as UTC via datetime('now'). The UI was
rendering them raw (e.g. "2026-05-18 15:42:03"), which is 5 hours
behind local time for Tajikistan.

Add formatTs() to the i18n store alongside formatMoney/localized.
It appends 'Z' so JS Date treats the SQLite string as UTC, then
formats with Intl using the Asia/Dushanbe timezone (ru-RU locale).

Replace all bare timestamp renders on:
- / (dashboard: recent movements created_at)
- /parts/[id] (part created_at, updated_at, movement history)
- /invoices/[id] (invoice saved_at on receipt)
- /admin/reports (recent sales saved_at; replaces local formatWhen)

Tested: UTC "2026-05-18 15:42:03" -> "18.05.2026, 20:42" (pass)
        UTC "2026-05-18 00:30:00" -> "18.05.2026, 05:30" (pass)
        null/empty/invalid input handled gracefully (pass)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 src/lib/i18n/store.js                      | 15 +++++++++++++++
 src/routes/+page.svelte                    |  2 +-
 src/routes/admin/reports/+page.svelte      |  9 +--------
 src/routes/invoices/[id]/+page.svelte      |  2 +-
 src/routes/parts/[id]/+page.svelte         |  4 ++--
 5 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/src/lib/i18n/store.js b/src/lib/i18n/store.js
--- a/src/lib/i18n/store.js
+++ b/src/lib/i18n/store.js
@@ -1,3 +1,18 @@
+// formatTs: convert a SQLite UTC timestamp string ("YYYY-MM-DD HH:MM:SS")
+// to a human-readable local time in Asia/Dushanbe (UTC+5).
+// The appended 'Z' is critical — without it JS parses as local time.
+export function formatTs(utcStr) {
+  if (!utcStr) return '';
+  const d = new Date(utcStr.replace(' ', 'T') + 'Z');
+  if (isNaN(d.getTime())) return utcStr;
+  return d.toLocaleString('ru-RU', {
+    timeZone: 'Asia/Dushanbe',
+    day:    '2-digit',
+    month:  '2-digit',
+    year:   'numeric',
+    hour:   '2-digit',
+    minute: '2-digit',
+  });
+}
+
diff --git a/src/routes/+page.svelte b/src/routes/+page.svelte
--- a/src/routes/+page.svelte
+++ b/src/routes/+page.svelte
@@ -1,6 +1,6 @@
 <script>
-  import { locale, t, localized } from '$lib/i18n/store.js';
+  import { locale, t, localized, formatTs } from '$lib/i18n/store.js';
 
   export let data;
   $: lang = $locale;
@@ -48,7 +48,7 @@
       {#each movements as m}
         <tr>
-          <td>{m.created_at}</td>
+          <td>{formatTs(m.created_at)}</td>
           <td><span class="pill">{$t('movements.type_' + m.movement_type)}</span></td>
           <td><a href="/parts/{m.part_id}">{localized(m, 'name', lang)}</a></td>
           <td class="num">{m.quantity}</td>

diff --git a/src/routes/admin/reports/+page.svelte b/src/routes/admin/reports/+page.svelte
--- a/src/routes/admin/reports/+page.svelte
+++ b/src/routes/admin/reports/+page.svelte
@@ -1,6 +1,6 @@
 <script>
-  import { locale, t, localized, formatMoney } from '$lib/i18n/store.js';
+  import { locale, t, localized, formatMoney, formatTs } from '$lib/i18n/store.js';
 
   export let data;
   $: lang = $locale;
   $: ({ sales, topParts, inventory, recentSales } = data);
 
-  function formatWhen(iso) {
-    if (!iso) return '';
-    const d = new Date(iso.replace(' ', 'T') + 'Z');
-    const pad = (n) => String(n).padStart(2, '0');
-    return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())} ${pad(d.getHours())}:${pad(d.getMinutes())}`;
-  }
 </script>
@@ -139,7 +132,7 @@
       {#each recentSales as s}
         <tr>
-          <td>{formatWhen(s.saved_at)}</td>
+          <td>{formatTs(s.saved_at)}</td>
           <td class="num">{s.line_count}</td>

diff --git a/src/routes/invoices/[id]/+page.svelte b/src/routes/invoices/[id]/+page.svelte
--- a/src/routes/invoices/[id]/+page.svelte
+++ b/src/routes/invoices/[id]/+page.svelte
@@ -1,6 +1,6 @@
 <script>
-  import { locale, t, localized, formatMoney } from '$lib/i18n/store.js';
+  import { locale, t, localized, formatMoney, formatTs } from '$lib/i18n/store.js';
 
   export let data;
   $: lang = $locale;
@@ -16,7 +16,7 @@
   <header class="head">
     <div>
       <h1>{$t('invoices.saved_title')} #{invoice.id}</h1>
-      <p class="muted">{invoice.saved_at}</p>
+      <p class="muted">{formatTs(invoice.saved_at)}</p>
     </div>

diff --git a/src/routes/parts/[id]/+page.svelte b/src/routes/parts/[id]/+page.svelte
--- a/src/routes/parts/[id]/+page.svelte
+++ b/src/routes/parts/[id]/+page.svelte
@@ -1,7 +1,7 @@
 <script>
   import { enhance } from '$app/forms';
-  import { locale, t, localized, formatMoney } from '$lib/i18n/store.js';
+  import { locale, t, localized, formatMoney, formatTs } from '$lib/i18n/store.js';
 
   export let data;
   export let form;
@@ -115,8 +115,8 @@
       <hr />
-      <div class="muted small">{$t('common.created')}: {part.created_at}</div>
-      <div class="muted small">{$t('common.updated')}: {part.updated_at}</div>
+      <div class="muted small">{$t('common.created')}: {formatTs(part.created_at)}</div>
+      <div class="muted small">{$t('common.updated')}: {formatTs(part.updated_at)}</div>
     </div>
@@ -131,7 +131,7 @@
           {#each movements as m}
             <tr>
-              <td>{m.created_at}</td>
+              <td>{formatTs(m.created_at)}</td>
               <td><span class="pill">{$t('movements.type_' + m.movement_type)}</span></td>