feat(packs): rewrite PackOpenService against per-pack draw table

Sampler is now driven by PackDrawTable: roll DrawTier per slot by
cumulative slot-rate weights, then pick a card within tier by per-card
weights renormalized within the tier. Rate-less Guaranteed-Leader-Card
rows draw uniform over (pool minus owned), falling back to the full
pool when all are owned. Bonus slot fires once at the end of a 10-pack
open when HasBonusSlot is set.

Slot 8 falls back to the general slot's per-card weights for the rolled
tier when slot-8 has only a rarity-level rate quoted (the common shape
on normal packs).

PackController.Open loads the draw table + viewer owned card ids and
passes them to the sampler; the category-based forced-Legendary slot-8
override is gone. ICardFoilLookup replaces ICardPoolProvider for the
foil-twin heuristic.

Drops the test-fixture pack-draw seed overlay so the production seed
flows through the importer tests; controller tests that fabricate their
own card sets now call factory.SeedPackDrawTableAsync(...) to install a
matching stub draw table.

WeightedPick helper handles the cumulative-band roll for both stages.
Five sampler tests + four WeightedPick tests + five importer/repo
tests; full suite is 653/653 green.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.UnitTests/Services/WeightedPickTests.cs

@@ -0,0 +1,63 @@
+using SVSim.Database.Services;
+using SVSim.EmulatedEntrypoint.Services;
+
+namespace SVSim.UnitTests.Services;
+
+public class WeightedPickTests
+{
+    private sealed class ScriptedRandom : IRandom
+    {
+        private readonly double[] _seq; private int _i;
+        public ScriptedRandom(params double[] seq) { _seq = seq; }
+        public double NextDouble() => _seq[_i++ % _seq.Length];
+        public int Next(int maxExclusive) => (int)(NextDouble() * maxExclusive);
+    }
+
+    [Test]
+    public void Picks_first_band_when_rng_low()
+    {
+        var items = new[] { "a", "b", "c" };
+        var weights = new[] { 0.5, 0.3, 0.2 };
+        var rng = new ScriptedRandom(0.1);
+
+        var picked = WeightedPick.Pick(rng, items, weights);
+
+        Assert.That(picked, Is.EqualTo("a"));
+    }
+
+    [Test]
+    public void Picks_middle_band()
+    {
+        var items = new[] { "a", "b", "c" };
+        var weights = new[] { 0.5, 0.3, 0.2 };
+        var rng = new ScriptedRandom(0.7);
+
+        var picked = WeightedPick.Pick(rng, items, weights);
+
+        Assert.That(picked, Is.EqualTo("b"));
+    }
+
+    [Test]
+    public void Renormalizes_when_weights_dont_sum_to_one()
+    {
+        var items = new[] { "a", "b" };
+        var weights = new[] { 50.0, 50.0 };
+        var rng = new ScriptedRandom(0.4);
+
+        var picked = WeightedPick.Pick(rng, items, weights);
+
+        Assert.That(picked, Is.EqualTo("a"));
+    }
+
+    [Test]
+    public void Falls_through_to_last_item_when_rng_exceeds_sum_minus_epsilon()
+    {
+        var items = new[] { "a", "b" };
+        var weights = new[] { 0.5, 0.5 };
+        var rng = new ScriptedRandom(0.999);
+
+        var picked = WeightedPick.Pick(rng, items, weights);
+
+        Assert.That(picked, Is.EqualTo("b"));
+    }
+}