feat: Finalizer-Agent – dritter Agent der nach Worker + Review einschreitet

Backend:
- SessionRecord + DB-Migration: finalizer_agent_id auf sessions
- ChatContext.FinalizerContext (Model, SystemPrompt, Tools, Workspace)
- ChatService: FinalizerContext aufbauen (analog zu ReviewContext)
- AnthropicService: RunFinalizer() nach Review-Phase (oder direkt nach Worker)
- RunReviewAgentChat() refactored zu generischem RunAgentChat()
  mit agentType-Parameter ('review' | 'finalizer') für SSE-Events und DB-Tags
- SSE-Events: finalizer_start, finalizer_text, finalizer_tool_use, finalizer_done

Frontend:
- Session-Page: Finalizer-Agent-Picker (im 'Weitere Einstellungen' Bereich)
- Chat: SSE-Events für Finalizer-Phase verarbeiten
- UI: addReviewBubble/finalizeReviewBubble unterstützen agentType 'finalizer'
  mit eigener Farbe (success-green) und Flag-Checkered-Icon
- renderMarkdown: [Finalizer: AgentName] Tags parsen
- History: Finalizer-Messages als .finalizer-bubble rendern
- Shared-Page: Finalizer-Messages korrekt erkennen und stylen
- Dashboard: Finalizer-Badge (flag-checkered) auf Session-Cards

Services/DatabaseService.cs

@@ -177,6 +177,7 @@ public class DatabaseService
         TryAddColumn(conn, "sessions", "avatar_offset_y", "REAL NOT NULL DEFAULT 0");
         TryAddColumn(conn, "agents", "avatar_offset_x", "REAL NOT NULL DEFAULT 0");
         TryAddColumn(conn, "agents", "avatar_offset_y", "REAL NOT NULL DEFAULT 0");
+        TryAddColumn(conn, "sessions", "finalizer_agent_id", "TEXT");
 
         conn.Execute(@"
             CREATE TABLE IF NOT EXISTS agent_skills (
@@ -373,7 +374,7 @@ public class DatabaseService
 
     // ── Sessions ──
 
-    public async Task<SessionRecord> CreateSession(string userId, string name = null, string description = null, string image = null, string agentId = null, string workspace = null, string context = null, string customCommands = null, double avatarScale = 1.0, double avatarOffsetX = 0, double avatarOffsetY = 0, string reviewAgentId = null, int maxReviewIterations = 3)
+    public async Task<SessionRecord> CreateSession(string userId, string name = null, string description = null, string image = null, string agentId = null, string workspace = null, string context = null, string customCommands = null, double avatarScale = 1.0, double avatarOffsetX = 0, double avatarOffsetY = 0, string reviewAgentId = null, int maxReviewIterations = 3, string finalizerAgentId = null)
     {
         using var conn = CreateConnection();
         var now = DateTime.UtcNow.ToString("o");
@@ -393,12 +394,13 @@ public class DatabaseService
             AvatarOffsetY = avatarOffsetY,
             ReviewAgentId = reviewAgentId,
             MaxReviewIterations = maxReviewIterations,
+            FinalizerAgentId = finalizerAgentId,
             CreatedAt = now,
             UpdatedAt = now
         };
         await conn.ExecuteAsync(@"
-            INSERT INTO sessions (session_id, user_id, name, description, image, agent_id, workspace, context, custom_commands, avatar_scale, avatar_offset_x, avatar_offset_y, review_agent_id, max_review_iterations, created_at, updated_at)
-            VALUES (@SessionId, @UserId, @Name, @Description, @Image, @AgentId, @Workspace, @Context, @CustomCommands, @AvatarScale, @AvatarOffsetX, @AvatarOffsetY, @ReviewAgentId, @MaxReviewIterations, @CreatedAt, @UpdatedAt)
+            INSERT INTO sessions (session_id, user_id, name, description, image, agent_id, workspace, context, custom_commands, avatar_scale, avatar_offset_x, avatar_offset_y, review_agent_id, max_review_iterations, finalizer_agent_id, created_at, updated_at)
+            VALUES (@SessionId, @UserId, @Name, @Description, @Image, @AgentId, @Workspace, @Context, @CustomCommands, @AvatarScale, @AvatarOffsetX, @AvatarOffsetY, @ReviewAgentId, @MaxReviewIterations, @FinalizerAgentId, @CreatedAt, @UpdatedAt)
         ", session);
         return session;
     }
@@ -446,6 +448,7 @@ public class DatabaseService
                 s.AvatarOffsetY,
                 s.ReviewAgentId,
                 s.MaxReviewIterations,
+                s.FinalizerAgentId,
                 s.IsDeleted,
                 s.CreatedAt,
                 s.UpdatedAt,
@@ -500,6 +503,7 @@ public class DatabaseService
         if (body.TryGetProperty("avatarOffsetY", out var aoy)) { sets.Add("avatar_offset_y = @avatarOffsetY"); p.Add("avatarOffsetY", aoy.GetDouble()); }
         if (body.TryGetProperty("reviewAgentId", out var ra)) { sets.Add("review_agent_id = @reviewAgentId"); p.Add("reviewAgentId", ra.ValueKind == System.Text.Json.JsonValueKind.Null ? null : ra.GetString()); }
         if (body.TryGetProperty("maxReviewIterations", out var mri)) { sets.Add("max_review_iterations = @maxReviewIterations"); p.Add("maxReviewIterations", mri.GetInt32()); }
+        if (body.TryGetProperty("finalizerAgentId", out var fa)) { sets.Add("finalizer_agent_id = @finalizerAgentId"); p.Add("finalizerAgentId", fa.ValueKind == System.Text.Json.JsonValueKind.Null ? null : fa.GetString()); }
 
         await conn.ExecuteAsync($"UPDATE sessions SET {string.Join(", ", sets)} WHERE session_id = @sessionId", p);
     }