feat(arena-colosseum): lobby + constructed entry (phase 1)

Closes 5 of arena-colosseum's 16 spec shapes (1/16 → 6/16). Lobby reads
(/top, /get_fee_info, /event_info) render an empty "no event scheduled"
payload by default; /entry + /register_deck activate via admin-flipped
ColosseumSeason + ColosseumRounds config sections.

* Schema: ViewerArenaColosseumRun standalone table (unique on ViewerId)
  with jsonb run-state columns mirroring ViewerArenaTwoPickRun.
* Config sections: ColosseumSeasonConfig (event-level), ColosseumRoundsConfig
  (the 3-round bracket). Empty defaults — IsColosseumPeriod=false.
* Migration AddArenaColosseumRun (DDL only; seed rows come from the section
  ShippedDefaults via EnsureSeedDataAsync).
* DTOs: ColosseumLobbyInfo (round-level, /top + /get_fee_info), ColosseumEventInfo
  (event-level, /event_info), ColosseumOwnStatus (shared status block),
  ColosseumEntryRef, ColosseumFeeList, ColosseumUserDeck, ColosseumBattleResults,
  ColosseumRoundDetail + ColosseumGroupRow. EventInfoResponse uses explicit
  [JsonPropertyName("1"|"2"|"3")] for the string-keyed rounds shape per spec.
* Controller: ArenaColosseumController replaces the 1-action stub with
  the five lifecycle endpoints. /top emits leader_skin_id even when 0
  (project_wire_null_policy override).
* Tests: 11 controller-level tests + 6 config round-trip tests covering
  empty-season payloads, run-seeded /top round-trip, crystal/rupy entry
  debits, now_round_id mismatch rejection, deck_no_list round-trip + reject.

SVSim.EmulatedEntrypoint/Models/Dtos/Requests/ArenaColosseum/ArenaColosseumRegisterDeckRequest.cs

@@ -0,0 +1,22 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.ArenaColosseum;
+
+/// <summary>
+/// <c>POST /arena_colosseum/register_deck</c> — submit deck slot(s) for a constructed-format
+/// entry. Same wire gotcha as <c>arena_competition/register_deck</c> et al — <see cref="DeckNoList"/>
+/// is a JSON-encoded STRING like <c>"[3,4,5]"</c>, not an array. The server parses it.
+/// </summary>
+[MessagePackObject(keyAsPropertyName: false)]
+public class ArenaColosseumRegisterDeckRequest : BaseRequest
+{
+    /// <summary>JSON-encoded list of deck slot numbers. Client does <c>JsonMapper.ToJson(List&lt;int&gt;)</c>.</summary>
+    [JsonPropertyName("deck_no_list")] [Key("deck_no_list")]
+    public string DeckNoList { get; set; } = "[]";
+
+    /// <summary>Server-stored visibility flag — does not affect bracket play.</summary>
+    [JsonPropertyName("is_published")] [Key("is_published")]
+    public bool IsPublished { get; set; }
+}