Combat tracker: multiple named encounters

- Encounter entity; Combatant now belongs to an encounter (ON DELETE
  CASCADE). Migration adds encounter_id, rehoming any existing combatants.
- /tracker lists encounters (name, count, last updated) with a "New
  encounter" form; /tracker/{id} is the HP tracker for one encounter.
- Encounters can be renamed, have their combatants cleared, or be deleted.
- The Enemies list gains an encounter picker next to "Add to tracker"
  (existing encounter or "— New encounter —", which prompts for a name);
  an encounter's "Add enemies" link pre-selects it via ?encounter=.
- Routes for combatant HP/remove moved under /tracker/combatant/ to keep
  the numeric {id} for encounters.

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

src/Entity/Combatant.php

@@ -19,6 +19,10 @@ class Combatant
     #[ORM\Column]
     private ?int $id = null;
 
+    #[ORM\ManyToOne(targetEntity: Encounter::class, inversedBy: 'combatants')]
+    #[ORM\JoinColumn(name: 'encounter_id', nullable: false, onDelete: 'CASCADE')]
+    private ?Encounter $encounter = null;
+
     #[ORM\ManyToOne(targetEntity: Enemy::class)]
     #[ORM\JoinColumn(name: 'enemy_id', onDelete: 'SET NULL', nullable: true)]
     private ?Enemy $enemy = null;
@@ -73,6 +77,18 @@ class Combatant
         return $this->id;
     }
 
+    public function getEncounter(): ?Encounter
+    {
+        return $this->encounter;
+    }
+
+    public function setEncounter(?Encounter $encounter): static
+    {
+        $this->encounter = $encounter;
+
+        return $this;
+    }
+
     public function getEnemy(): ?Enemy
     {
         return $this->enemy;

src/Entity/Encounter.php

@@ -0,0 +1,102 @@
+<?php
+
+namespace App\Entity;
+
+use App\Repository\EncounterRepository;
+use Doctrine\Common\Collections\ArrayCollection;
+use Doctrine\Common\Collections\Collection;
+use Doctrine\DBAL\Types\Types;
+use Doctrine\ORM\Mapping as ORM;
+use Symfony\Component\Validator\Constraints as Assert;
+
+/**
+ * A named combat: a list of combatants with their HP, kept for prep and reuse.
+ */
+#[ORM\Entity(repositoryClass: EncounterRepository::class)]
+#[ORM\Table(name: 'encounter')]
+#[ORM\HasLifecycleCallbacks]
+class Encounter
+{
+    #[ORM\Id]
+    #[ORM\GeneratedValue]
+    #[ORM\Column]
+    private ?int $id = null;
+
+    #[ORM\Column(length: 120)]
+    #[Assert\NotBlank]
+    private string $name = '';
+
+    #[ORM\Column(type: Types::DATETIME_IMMUTABLE)]
+    private \DateTimeImmutable $createdAt;
+
+    #[ORM\Column(type: Types::DATETIME_IMMUTABLE)]
+    private \DateTimeImmutable $updatedAt;
+
+    /** @var Collection<int, Combatant> */
+    #[ORM\OneToMany(mappedBy: 'encounter', targetEntity: Combatant::class, cascade: ['persist', 'remove'], orphanRemoval: true)]
+    #[ORM\OrderBy(['position' => 'ASC', 'id' => 'ASC'])]
+    private Collection $combatants;
+
+    public function __construct()
+    {
+        $this->createdAt = new \DateTimeImmutable();
+        $this->updatedAt = new \DateTimeImmutable();
+        $this->combatants = new ArrayCollection();
+    }
+
+    #[ORM\PreUpdate]
+    public function touch(): void
+    {
+        $this->updatedAt = new \DateTimeImmutable();
+    }
+
+    public function getId(): ?int
+    {
+        return $this->id;
+    }
+
+    public function getName(): string
+    {
+        return $this->name;
+    }
+
+    public function setName(string $name): static
+    {
+        $this->name = $name;
+
+        return $this;
+    }
+
+    public function getCreatedAt(): \DateTimeImmutable
+    {
+        return $this->createdAt;
+    }
+
+    public function getUpdatedAt(): \DateTimeImmutable
+    {
+        return $this->updatedAt;
+    }
+
+    /** @return Collection<int, Combatant> */
+    public function getCombatants(): Collection
+    {
+        return $this->combatants;
+    }
+
+    public function addCombatant(Combatant $combatant): static
+    {
+        if (!$this->combatants->contains($combatant)) {
+            $this->combatants->add($combatant);
+            $combatant->setEncounter($this);
+        }
+
+        return $this;
+    }
+
+    public function removeCombatant(Combatant $combatant): static
+    {
+        $this->combatants->removeElement($combatant);
+
+        return $this;
+    }
+}