Reorganise by feature, rename to Novelly, add Aspire and a pre-push hook

The layered split into Domain/Application/Infrastructure/Api was forcing
organisation by layer: adding one capability meant touching four projects and
four folders that each held a slice of it. Those four projects are now one
feature-organised Novelly.Api, where each folder — Projects, Characters,
Chapters, Beats, Scenes, Tags, Agent — holds its entity, DTOs, service and
endpoints together. Common/ holds what genuinely crosses features (the patch
semantics, the two exception types, DraftStatus) and Data/ holds the DbContext
and migrations.

Six .NET projects become five: the three layer projects are gone, and
Novelly.AppHost and Novelly.ServiceDefaults are new.

- Namespaces move from NovelSoftware.* to Novelly.*, including the entity type
  names recorded in the EF model snapshots. The migration ids are untouched, so
  an existing novel.db still migrates cleanly — verified against a fresh file.
- Aspire orchestration mirrors the mic-check setup: the AppHost starts the API
  on :5080 and the Vite dev server on :5173, and the API picks up OpenTelemetry,
  health checks and service discovery from ServiceDefaults. /health and /alive
  now answer in development.
- A Husky pre-push hook runs scripts/ci/prepush.sh: build, test, then a web
  build. The scripts are plain bash so CI can run the same steps.
- The MCP server's env var is now NOVELLY_API_URL.

Verified beyond the build: 44 tests pass, the web client builds, the API was
exercised over curl (project/chapter/beat/tag round trip, tag cross-reference,
503 on the agent without a key while conversation listing still returns 200),
the MCP server was driven over stdio JSON-RPC (26 tools, errors still surface
the API's own message rather than being flattened), and the AppHost was run to
confirm both resources come up and Vite proxies /api through to the API.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S56bfZMGe1hnhpWP4CjjNw

tests/Novelly.Api.Tests/AnthropicClientTests.cs

@@ -0,0 +1,38 @@
+using Microsoft.Extensions.Options;
+using Novelly.Api.Agent;
+using Novelly.Api.Common;
+
+namespace Novelly.Api.Tests;
+
+[TestFixture]
+public class AnthropicClientTests
+{
+    [Test]
+    public void Constructing_without_a_key_does_not_throw() =>
+        // The agent service takes this as a dependency and also serves read-only endpoints
+        // (listing conversations, reading a transcript). Throwing at construction would
+        // take those down on any install that has not configured a key yet.
+        Assert.That(
+            () => new AnthropicAgentModelClient(Options.Create(new AgentOptions())),
+            Throws.Nothing);
+
+    [Test]
+    public void Sending_without_a_key_reports_a_configuration_problem()
+    {
+        var previous = Environment.GetEnvironmentVariable("ANTHROPIC_API_KEY");
+        Environment.SetEnvironmentVariable("ANTHROPIC_API_KEY", null);
+
+        try
+        {
+            var client = new AnthropicAgentModelClient(Options.Create(new AgentOptions()));
+
+            Assert.That(
+                async () => await client.CompleteAsync("system", [], []),
+                Throws.TypeOf<AgentNotConfiguredException>().With.Message.Contains("ANTHROPIC_API_KEY"));
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable("ANTHROPIC_API_KEY", previous);
+        }
+    }
+}