chore(data): remove raw ADO.NET infrastructure, add EF migration and design-time factory

Delete SqliteConnectionFactory, SchemaInitializer, and schema.sql.
Fix ValueConverter lambdas in entity configurations (no throw-expressions
in expression trees). Add IDesignTimeDbContextFactory for dotnet-ef tooling.
Generate InitialCreate migration with seed data for agent/manual tags.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Data/ClaudeDoDbContextFactory.cs

@@ -0,0 +1,15 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Design;
+
+namespace ClaudeDo.Data;
+
+public sealed class ClaudeDoDbContextFactory : IDesignTimeDbContextFactory<ClaudeDoDbContext>
+{
+    public ClaudeDoDbContext CreateDbContext(string[] args)
+    {
+        var options = new DbContextOptionsBuilder<ClaudeDoDbContext>()
+            .UseSqlite("Data Source=design-time.db")
+            .Options;
+        return new ClaudeDoDbContext(options);
+    }
+}