Add novel-writing app: .NET 10 API, React front end, agent and MCP server

Builds out the vertical slice for planning and writing a novel. Three front
ends — the React UI, an embedded Claude agent, and an MCP stdio server — all go
through one REST API, so an edit made from Claude Code and one made in the
browser are the same edit.

Layout:
  Domain          entities and enums, no dependencies
  Application     services, DTOs, the agent tool-use loop and its 15 tools
  Infrastructure  EF Core 10 + SQLite, Anthropic SDK client
  Api             ASP.NET Core 10 minimal APIs, OpenAPI, ProblemDetails
  Mcp             MCP stdio server, 21 tools over the same REST API
  Web             React 19 + Vite + TanStack Query + Tailwind v4

Data model is Project > Characters / OutlineNodes / Chapters > Scenes, plus
agent conversations. The outline is a self-nesting tree so acts, sequences and
beats can be arranged however the book wants; scenes carry goal/conflict/outcome
because that is what the agent drafts prose from.

Notes on a few choices:

- Conversation history replays to the model as text only. The agent re-reads
  current state through its tools rather than trusting a record of edits that
  may since have changed in the UI.
- The user's turn is persisted before the tool loop runs, so a question is
  recorded even when the model call fails. Turn order uses an explicit sequence
  column; timestamps tie when a turn completes inside one tick.
- Tool failures return is_error results rather than throwing, so the model can
  read the message and correct itself. MCP tools do the same via CallToolResult,
  which keeps the API's own message instead of a generic SDK error.
- The Anthropic client is constructed lazily. It is injected into the agent
  service, which also serves read-only endpoints, and those should keep working
  on an install with no key. Sending without one returns 503, not 400.
- DateTimeOffset is stored as UTC ticks. SQLite refuses to ORDER BY the default
  text form, which every "recently updated first" listing depends on.

Tests run against real in-memory SQLite rather than the EF in-memory provider so
they exercise the cascade deletes and query translation that actually ship.

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

src/NovelSoftware.Domain/Entities/Character.cs

@@ -0,0 +1,62 @@
+namespace NovelSoftware.Domain.Entities;
+
+/// <summary>
+/// A character dossier. Every field beyond <see cref="Name"/> is optional so a writer can
+/// start with a name and fill the sheet in as the character comes into focus.
+/// </summary>
+public class Character
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+    public Guid ProjectId { get; set; }
+    public Project? Project { get; set; }
+
+    public string Name { get; set; } = string.Empty;
+    public CharacterRole Role { get; set; } = CharacterRole.Supporting;
+
+    public string? Age { get; set; }
+    public string? Pronouns { get; set; }
+    public string? Occupation { get; set; }
+
+    public string? Appearance { get; set; }
+    public string? Personality { get; set; }
+    public string? Backstory { get; set; }
+
+    /// <summary>What the character consciously wants.</summary>
+    public string? Want { get; set; }
+
+    /// <summary>What the character actually needs — usually at odds with <see cref="Want"/>.</summary>
+    public string? Need { get; set; }
+
+    public string? InternalConflict { get; set; }
+    public string? ExternalConflict { get; set; }
+
+    /// <summary>How the character changes over the course of the book.</summary>
+    public string? ArcSummary { get; set; }
+
+    /// <summary>Speech patterns, verbal tics, register — anything that makes dialogue sound like them.</summary>
+    public string? Voice { get; set; }
+
+    public string? Notes { get; set; }
+
+    public DateTimeOffset CreatedAt { get; set; } = DateTimeOffset.UtcNow;
+    public DateTimeOffset UpdatedAt { get; set; } = DateTimeOffset.UtcNow;
+
+    public List<CharacterRelationship> Relationships { get; set; } = [];
+}
+
+/// <summary>A directed relationship from one character to another.</summary>
+public class CharacterRelationship
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    public Guid CharacterId { get; set; }
+    public Character? Character { get; set; }
+
+    public Guid RelatedCharacterId { get; set; }
+    public Character? RelatedCharacter { get; set; }
+
+    /// <summary>e.g. "sister", "rival", "former mentor".</summary>
+    public string RelationshipType { get; set; } = string.Empty;
+
+    public string? Description { get; set; }
+}