feat(mosstank): the button is Force Buff — always recast everything

Virindi Tank's own term: Force Buff recasts the lot rather than only what has
lapsed. The button now does that, and says so.

BuffPlan gained a force flag that skips the already-in-force check. Forcing
means "ignore what is already up", NOT "ignore the settings" -- the trained-
skill filter, the attribute toggle and the difficulty margin all still apply,
and there is a test pinning that.

The loop had to change shape for this. It used to re-derive the plan every
tick and treat "plan is empty" as done, which works only because the ordinary
plan shrinks as buffs land. A forced plan never shrinks -- that is the point --
so the same loop would have cast forever. A pass now captures a queue at the
start and works through it by index, which is also cheaper: no rebuilding 80-odd
buff lines every frame.

A spell that will not go now advances the queue rather than blocking it. One
missing component used to mean everything behind it waited for the stall
timeout; now the status line names the refusal and the pass carries on.

Solution builds clean; 14,440 tests pass on the standard hermetic lane filter,
0 failures.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/AcDream.Plugins.MossTank.Tests/BuffPlanTests.cs

@@ -202,6 +202,40 @@ public class BuffPlanTests
         Assert.Equal(new uint[] { 2, 3, 1 }, plan.Select(s => s.SpellId).ToArray());
     }
 
+    [Fact]
+    public void ForceQueuesBuffsThatAreAlreadyInForce()
+    {
+        // Virindi Tank's Force Buff recasts everything rather than only what
+        // has lapsed, which is what the Buff button does.
+        var lines = Lines(
+            Spell(1, 47, 4, "Increases the caster's Life Magic skill by 10 points.",
+                difficulty: 100, school: LifeMagicSkill));
+        var skills = new[] { Skill(LifeMagicSkill, "Life Magic", PluginSkillTraining.Trained) };
+        var active = new[] { new PluginActiveEnchantment(1, 47, 4, 1800) };
+
+        Assert.Empty(BuffPlan.Build(lines, skills, Array.Empty<PluginAttributeInfo>(),
+            active, Default));
+        Assert.Single(BuffPlan.Build(lines, skills, Array.Empty<PluginAttributeInfo>(),
+            active, Default, force: true));
+    }
+
+    [Fact]
+    public void ForceStillRespectsSkillAndTrainingFilters()
+    {
+        // Forcing means "ignore what is already up", not "ignore the settings".
+        var lines = Lines(
+            Spell(1, 71, 1, "Increases the caster's Leadership skill by 10 points."));
+
+        var plan = BuffPlan.Build(
+            lines,
+            new[] { Skill(35, "Leadership", PluginSkillTraining.Untrained) },
+            Array.Empty<PluginAttributeInfo>(),
+            Array.Empty<PluginActiveEnchantment>(),
+            Default, force: true);
+
+        Assert.Empty(plan);
+    }
+
     [Fact]
     public void EmptySpellbookProducesNoPlan()
     {