Posts for later, hashtags followed, and Explore

The composer's clock button gives a post a time (scheduled_at, at least five
minutes ahead; located and group posts have none), and /scheduled moves or
drops what waits. A hashtag's feed tab shows its week and follows it, so its
public posts come home. Explore (/explore) shows what PrivaPub says is
trending, hashtags, posts and links from public posts it holds, the
directory by activity or by joining, and the hashtags the persona follows.
DiscoveryService does the calls; the e2e tests check each against PrivaPub's
own answer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

Models/ComposeForm.cs

@@ -37,6 +37,14 @@ public class ComposeForm
 	public double? Latitude { get; set; }
 	public double? Longitude { get; set; }
 
+	/// <summary>Whether the post waits for ScheduledAt (a datetime-local value, the reader's own time) instead of going now.</summary>
+	public bool IsScheduled { get; set; }
+	public string ScheduledAt { get; set; }
+
+	/// <summary>When the post is to be published, in UTC, or null when it goes now or ScheduledAt is not a time.</summary>
+	public DateTime? ScheduledAtUtc => IsScheduled && DateTime.TryParse(ScheduledAt, System.Globalization.CultureInfo.InvariantCulture,
+		System.Globalization.DateTimeStyles.AssumeLocal, out var local) ? local.ToUniversalTime() : null;
+
 	[JsonIgnore, Bindable(false)]
 	public MediaType MediaType { get; set; } = MediaType.Images;
 	[JsonIgnore, Bindable(false)]