Unify MCP and agent tool surfaces onto one registry in NovelAgentToolset

Fixes NovelAgentService continuing a conversation under the wrong
novel's route, since FindConversationAsync matched by id alone. Then
extends NovelAgentToolset to all 45 tools the stdio MCP server offered
(tag/location CRUD, character relationships, arc-stage beat pinning,
question editing, cross-novel novel listing/creation), tagging each
with whether it needs an explicit novel scope so a later MCP adapter
can inject it. Renames the toolset's 33 existing schemas from
snake_case to camelCase to match .NET/REST convention, since nothing
external consumes them.

Lays the groundwork to serve this same registry over MCP at /mcp and
retire the separate stdio Novelly.Mcp project (docs/plans/api/mcp_http_merge_plan.md).

tests/Novelly.Api.Tests/NovelAgentServiceTests.cs

@@ -100,7 +100,7 @@ public class NovelAgentServiceTests : ServiceTestFixture
         var novelId = (await Novels.CreateAsync(new CreateNovelRequest("The Salt Road"))).Id;
 
         var model = new ScriptedModelClient([
-            [ToolUse("t1", "update_character", new { character_id = Guid.NewGuid().ToString(), name = "Ines" })],
+            [ToolUse("t1", "update_character", new { characterId = Guid.NewGuid().ToString(), name = "Ines" })],
             [new AgentTextBlock("That character does not exist yet — shall I create her?")]
         ]);
 
@@ -185,6 +185,42 @@ public class NovelAgentServiceTests : ServiceTestFixture
         });
     }
 
+    [Test]
+    public async Task Continuing_a_conversation_under_a_different_novel_is_rejected()
+    {
+        var novelAId = (await Novels.CreateAsync(new CreateNovelRequest("The Salt Road"))).Id;
+        var novelBId = (await Novels.CreateAsync(new CreateNovelRequest("A Different Book"))).Id;
+        var model = new ScriptedModelClient([
+            [new AgentTextBlock("First answer.")]
+        ]);
+        var agent = BuildAgent(model);
+
+        var first = await agent.SendMessageAsync(novelAId, new SendAgentMessageRequest("Question one."));
+
+        var second = await agent.SendMessageAsync(
+            novelBId, new SendAgentMessageRequest("Question two.", first.ConversationId));
+
+        Assert.That(second, Is.Null);
+    }
+
+    [Test]
+    public async Task Continuing_a_conversation_under_its_own_novel_still_works()
+    {
+        var novelId = (await Novels.CreateAsync(new CreateNovelRequest("The Salt Road"))).Id;
+        var model = new ScriptedModelClient([
+            [new AgentTextBlock("First answer.")],
+            [new AgentTextBlock("Second answer.")]
+        ]);
+        var agent = BuildAgent(model);
+
+        var first = await agent.SendMessageAsync(novelId, new SendAgentMessageRequest("Question one."));
+        var second = await agent.SendMessageAsync(
+            novelId, new SendAgentMessageRequest("Question two.", first.ConversationId));
+
+        Assert.That(second, Is.Not.Null);
+        Assert.That(second.ConversationId, Is.EqualTo(first.ConversationId));
+    }
+
     [Test]
     public void Every_tool_declares_an_object_schema_and_a_description()
     {