docs(battle-node): project README + docstrings on hosting/lifecycle

Add a per-project README in SVSim.BattleNode/ that covers:
- Architecture (the six concern folders)
- The connect-handshake sequence verified end-to-end at smoke
- A wire-format-gotchas table for the spec divergences caught during
  v1 (headers vs query for credentials, schemeless node URL with
  /socket.io/ path, required card_master_id, required resultCode=1,
  Matched in response to InitBattle not InitNetwork, EIO3 0x04 prefix
  on binary frames, FromJson conditional-expression number-boxing)
- What the v1 scripted opponent does and what is hardcoded
- A "where to extend" table for v2 work
- The full test layout and cross-references to specs/plans

Fill in XML docs on the public surface that previously had none:
- BattleNodeExtensions.AddBattleNode / UseBattleNode (DI + middleware
  wiring, including the pipeline-order note that auth runs before
  UseWebSockets)
- BattleNodeWebSocketHandler class + HandleAsync (the validation chain)
- BattleSession.ComputeResponses (the lifecycle state machine, with
  the NoStock flag's meaning)
- ScriptedLifecycle class (v1 scope, resultCode injection rule,
  pointer to the "where to extend" section)
- MatchingBridge class (mint-id + register flow)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.BattleNode/Lifecycle/ScriptedLifecycle.cs

@@ -3,15 +3,38 @@ using SVSim.BattleNode.Protocol;
 namespace SVSim.BattleNode.Lifecycle;
 
 /// <summary>
-/// v1 Path-A scripted opponent. Hand-rolled static frames good enough to land the client on
-/// the mulligan screen and let them play turn 1. Templates derived from
-/// data_dumps/captures/battle-traffic_tk2_regular.ndjson.
+/// v1 hand-rolled scripted opponent. Static frame builders for the five lifecycle uris
+/// (Matched / BattleStart / Deal / Swap response / Ready) plus a trivial opponent TurnStart
+/// the dispatch pushes after the player's TurnEnd. The values are templated from the TK2
+/// captures at <c>data_dumps/captures/battle-traffic_tk2_regular.ndjson</c> — anything
+/// hardcoded here came from a real prod frame.
 /// </summary>
+/// <remarks>
+/// <para>"Scripted" means the opponent never reacts to your plays. We push enough to land
+/// you on the mulligan screen, run a real mulligan exchange, give you turn 1, transition
+/// to "Opponent's turn…" after your <c>TurnEnd</c>, and then sit there indefinitely. This
+/// is the documented v1 stopping point.</para>
+/// <para>
+/// All builders go through <see cref="EnvelopeForPush"/>, which injects
+/// <c>resultCode = 1</c> into every body. The client's <c>OnReceived</c> drops any
+/// synchronize push whose <c>resultCode != Success</c> (absent counts as None=0); leaving
+/// it off silently breaks the state machine without surfacing an error.
+/// </para>
+/// <para>To make this less scripted: see the project README §"Where to extend".</para>
+/// </remarks>
 public static class ScriptedLifecycle
 {
-    /// <summary>30 dummy cardIds — repeats of a stable neutral card.</summary>
+    /// <summary>
+    /// CardId used for all 30 entries in the dummy deck. A stable neutral card that exists in
+    /// every card-master version we care about, so the client can render it without
+    /// triggering a card-master-mismatch error.
+    /// </summary>
     public static readonly long DummyCardId = 100011010;
 
+    /// <summary>
+    /// Viewer id we present as the opponent on every scripted push. Out-of-range vs. real
+    /// viewer ids so it can't collide with a real account in the auth pipeline.
+    /// </summary>
     public const long FakeOpponentViewerId = 999_999_999L;
 
     public static MsgEnvelope BuildMatched(long playerViewerId, long opponentViewerId, string battleId)