feat: custom sync start time and frequency scheduling (#241)

* feat: add custom sync start time scheduling

* Updated UI

* docs: add updated issue 240 UI screenshot

* fix: improve schedule UI with client-side next run calc and timezone handling

- Compute next scheduled run client-side via useMemo to avoid permanent
  "Calculating..." state when server hasn't set nextRun yet
- Default to browser timezone when enabling syncing (not UTC)
- Show actual saved timezone in badge, use it consistently in all handlers
- Match time input background to select trigger in dark mode
- Add clock icon to time picker with hidden native indicator

src/pages/api/job/schedule-sync-repo.ts

@@ -8,7 +8,7 @@ import type {
   ScheduleSyncRepoResponse,
 } from "@/types/sync";
 import { createSecureErrorResponse } from "@/lib/utils";
-import { parseInterval } from "@/lib/utils/duration-parser";
+import { getNextScheduledRun, normalizeTimezone } from "@/lib/utils/schedule-utils";
 import { requireAuthenticatedUserId } from "@/lib/auth-guards";
 
 export const POST: APIRoute = async ({ request, locals }) => {
@@ -68,17 +68,17 @@ export const POST: APIRoute = async ({ request, locals }) => {
 
     // Calculate nextRun and update lastRun and nextRun in the config
     const currentTime = new Date();
-    let intervalMs = 3600 * 1000;
+    const scheduleSource =
+      config.scheduleConfig?.interval ||
+      config.giteaConfig?.mirrorInterval ||
+      "3600";
+    const timezone = normalizeTimezone(config.scheduleConfig?.timezone || "UTC");
+    let nextRun = new Date(currentTime.getTime() + 3600 * 1000);
     try {
-      intervalMs = parseInterval(
-        typeof config.scheduleConfig?.interval === 'number'
-          ? config.scheduleConfig.interval
-          : (config.scheduleConfig?.interval as unknown as string) || '3600'
-      );
+      nextRun = getNextScheduledRun(scheduleSource, currentTime, timezone);
     } catch {
-      intervalMs = 3600 * 1000;
+      nextRun = new Date(currentTime.getTime() + 3600 * 1000);
     }
-    const nextRun = new Date(currentTime.getTime() + intervalMs);
 
     // Update the full giteaConfig object
     await db