feat(guild_chat): messages window + system events

- GuildChatService.EmitSystemEventAsync: replaces no-op stub with real
  chat-row insertion via _msgs.AppendAsync (per-guild monotonic id).
- GuildChatService.GetWindowAsync: real implementation — verifies caller
  membership, delegates to IGuildChatMessageRepository.GetWindowAsync
  (direction 1=OLD/2=NEW/3=BOTH, limit 50), returns adaptive wait interval
  (ChatPollActiveSeconds when messages returned, ChatPollIdleSeconds otherwise).
- Drop unused repo injections from GuildChatService (guilds, invites, joinRequests).
- GuildChatController.Messages: wires the full response — chat_message[],
  users[] (deduplicated author profiles with Emblem+Degree nav includes),
  maintenance_card_list (empty until maintenance service lands), wait_interval.
- GuildChatPollTests (7 integration tests): fresh-guild CreateGuild event,
  sequenced Create+Join ordering, direction=NEW filter, direction=BOTH window,
  users[] deduplication, empty result for viewer-not-in-guild, active vs idle
  interval comparison. All 7 pass; full suite 1515/1515.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Controllers/GuildChatController.cs

@@ -1,6 +1,9 @@
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using SVSim.Database;
 using SVSim.Database.Services.Guild;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Common;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Common.Guild;
 using SVSim.EmulatedEntrypoint.Models.Dtos.GuildChat;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
 
@@ -11,18 +14,76 @@ namespace SVSim.EmulatedEntrypoint.Controllers;
 public sealed class GuildChatController : SVSimController
 {
     private readonly IGuildChatService _chat;
+    private readonly SVSimDbContext _db;
 
-    public GuildChatController(IGuildChatService chat) => _chat = chat;
+    public GuildChatController(IGuildChatService chat, SVSimDbContext db)
+    {
+        _chat = chat;
+        _db   = db;
+    }
 
     [HttpPost("messages")]
-    public Task<ActionResult<GuildChatMessagesResponse>> Messages([FromBody] GuildChatMessagesRequest req, CancellationToken ct)
-        => Task.FromResult<ActionResult<GuildChatMessagesResponse>>(new GuildChatMessagesResponse
+    public async Task<ActionResult<GuildChatMessagesResponse>> Messages(
+        [FromBody] GuildChatMessagesRequest req,
+        CancellationToken ct)
+    {
+        if (!TryGetViewerId(out var viewerId)) return Unauthorized();
+
+        var window = await _chat.GetWindowAsync(
+            viewerId,
+            (int)req.StartMessageId,
+            req.Direction,
+            req.WaitInterval,
+            ct);
+
+        // Build chat_message list
+        var chatMessages = window.Messages.Select(m => new ChatMessageDto
+        {
+            ViewerId    = m.AuthorViewerId,
+            MessageId   = m.MessageId,
+            MessageType = (int)m.MessageType,
+            CreateTime  = new DateTimeOffset(m.CreatedAt, TimeSpan.Zero).ToUnixTimeSeconds(),
+            Message     = m.Body,
+            // deck / replay / room remain null until Task 17
+        }).ToList();
+
+        // Build deduplicated users[] catalog from message authors
+        var authorIds = window.Messages
+            .Select(m => m.AuthorViewerId)
+            .Distinct()
+            .ToList();
+
+        var viewers = authorIds.Count == 0
+            ? new Dictionary<long, SVSim.Database.Models.Viewer>()
+            : await _db.Viewers
+                .AsNoTracking()
+                .Include(v => v.Info.SelectedEmblem)
+                .Include(v => v.Info.SelectedDegree)
+                .Where(v => authorIds.Contains(v.Id))
+                .ToDictionaryAsync(v => v.Id, ct);
+
+        var users = authorIds.Select(vid =>
+        {
+            viewers.TryGetValue(vid, out var v);
+            return new ChatUserDto
+            {
+                ViewerId    = vid,
+                Name        = v?.DisplayName ?? "",
+                EmblemId    = v?.Info?.SelectedEmblem?.Id is > 0 ? v.Info.SelectedEmblem.Id : 100_000_000L,
+                CountryCode = v?.Info?.CountryCode ?? "",
+                Rank        = 1, // TODO: real rank when rank tracking lands
+                DegreeId    = v?.Info?.SelectedDegree?.Id ?? 0,
+            };
+        }).ToList();
+
+        return new GuildChatMessagesResponse
         {
             MaintenanceCardList = new(),
-            Users = new(),
-            ChatMessage = new(),
-            WaitInterval = 10,
-        });
+            Users               = users,
+            ChatMessage         = chatMessages,
+            WaitInterval        = window.WaitIntervalSeconds,
+        };
+    }
 
     [HttpPost("post")]
     public Task<ActionResult<GuildChatPostResponse>> Post([FromBody] GuildChatPostRequest req, CancellationToken ct)