refactor(bootstrap): migrate practice opponents to seed file

Move /practice/info handling out of GlobalsImporter into a dedicated
PracticeOpponentImporter that reads a normalized JSON seed file
generated by data_dumps/extract/extract-practice-opponents.ps1.

SVSim.Bootstrap/Importers/PracticeOpponentImporter.cs

@@ -0,0 +1,54 @@
+using Microsoft.EntityFrameworkCore;
+using SVSim.Bootstrap.Models.Seed;
+using SVSim.Database;
+using SVSim.Database.Models;
+
+namespace SVSim.Bootstrap.Importers;
+
+/// <summary>
+/// Idempotent upsert of practice opponents from <c>seeds/practice-opponents.json</c>.
+/// Rows missing from the seed are LEFT INTACT (consistent with the previous import behavior;
+/// a partial seed shouldn't silently delete entries).
+/// </summary>
+public class PracticeOpponentImporter
+{
+    public async Task<int> ImportAsync(SVSimDbContext context, string seedDir)
+    {
+        string path = Path.Combine(seedDir, "practice-opponents.json");
+        var seed = SeedLoader.LoadList<PracticeOpponentSeed>(path);
+        if (seed.Count == 0)
+        {
+            Console.WriteLine("[PracticeOpponentImporter] No seed rows; skipping.");
+            return 0;
+        }
+
+        var existing = await context.PracticeOpponents.ToDictionaryAsync(e => e.Id);
+        int created = 0, updated = 0;
+
+        foreach (var s in seed)
+        {
+            if (s.PracticeId == 0) continue;
+
+            var entry = existing.TryGetValue(s.PracticeId, out var ex)
+                ? ex : new PracticeOpponentEntry { Id = s.PracticeId };
+
+            entry.TextId = s.TextId;
+            entry.ClassId = s.ClassId;
+            entry.CharaId = s.CharaId;
+            entry.DegreeId = s.DegreeId;
+            entry.AiDeckLevel = s.AiDeckLevel;
+            entry.AiLogicLevel = s.AiLogicLevel;
+            entry.AiMaxLife = s.AiMaxLife;
+            entry.Battle3dFieldId = s.Battle3dFieldId;
+            entry.IsMaintenance = s.IsMaintenance;
+            entry.IsCampaignPractice = s.IsCampaignPractice;
+
+            if (ex is null) { context.PracticeOpponents.Add(entry); created++; }
+            else updated++;
+        }
+
+        await context.SaveChangesAsync();
+        Console.WriteLine($"[PracticeOpponentImporter] +{created}/~{updated}");
+        return created + updated;
+    }
+}