M3: Agent bound to a seat — configure an AI seat

OrgBoard: Agent entity (name, monogram, autonomy dial, ApiConfigId + optional fallback,
skill keys, docs) + AddAgents migration; one agent per seat. References Skills by key and
the BYOK config by id — never reaches into those modules.

Endpoints: POST/GET /api/orgboard/seats (create/list seats), POST/GET
/api/orgboard/seats/{id}/agent (configure/read the agent) — ConfigureAgents at [team, org].
Configuring an agent flips the seat to the AI state and points it at the agent; audited.

Verified: build green; ArchitectureTests 8/8; IntegrationTests 27/27 incl. the M3 acceptance
flow — owner adds a BYOK config, then configures "Aria" (gated autonomy, skills, that config)
on a seat, flipping it to AI, with the key never exposed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Modules/TeamUp.Modules.OrgBoard/Domain/Agent.cs

@@ -0,0 +1,54 @@
+using TeamUp.SharedKernel.Access;
+using TeamUp.SharedKernel.Domain;
+
+namespace TeamUp.Modules.OrgBoard.Domain;
+
+/// <summary>
+/// The AI staffing an open seat: identity (name, monogram) + matched skill atoms + autonomy +
+/// the model config + docs. References Skills by key and the BYOK ApiConfig by id — never reaches
+/// into those modules' tables. One agent per seat.
+/// </summary>
+internal sealed class Agent : Entity
+{
+    public Guid SeatId { get; private set; }
+    public string Name { get; private set; } = null!;
+    public string? Monogram { get; private set; }
+    public Autonomy Autonomy { get; private set; }
+    public Guid ApiConfigId { get; private set; }
+    public Guid? FallbackApiConfigId { get; private set; }
+    public List<string> SkillKeys { get; private set; } = [];
+    public List<string> Docs { get; private set; } = [];
+    public DateTimeOffset CreatedAtUtc { get; private set; }
+    public DateTimeOffset UpdatedAtUtc { get; private set; }
+
+    private Agent()
+    {
+    }
+
+    public Agent(Guid seatId, DateTimeOffset createdAtUtc)
+    {
+        SeatId = seatId;
+        CreatedAtUtc = createdAtUtc;
+        UpdatedAtUtc = createdAtUtc;
+    }
+
+    public void Configure(
+        string name,
+        string? monogram,
+        Autonomy autonomy,
+        Guid apiConfigId,
+        Guid? fallbackApiConfigId,
+        List<string> skillKeys,
+        List<string> docs,
+        DateTimeOffset nowUtc)
+    {
+        Name = name;
+        Monogram = monogram;
+        Autonomy = autonomy;
+        ApiConfigId = apiConfigId;
+        FallbackApiConfigId = fallbackApiConfigId;
+        SkillKeys = skillKeys;
+        Docs = docs;
+        UpdatedAtUtc = nowUtc;
+    }
+}