feat(core): implement playable CTF prototype with 6 core scripts

Implements the minimal playable core for the teaser prototype:
- Game.cs: Bootstrap, scene setup, scoring, round reset, win condition
- Unit.cs: Movement, route following, tagging, respawn
- RouteDrawer.cs: Click-drag route input with LineRenderer preview
- Flag.cs: Pickup, drop, return mechanics
- Visibility.cs: Fog of war via SpriteRenderer visibility
- SimpleAI.cs: Enemy AI that chases player flag

All game objects created programmatically (no Editor setup required).
Uses RuntimeInitializeOnLoadMethod for automatic bootstrap.

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

Backyard CTF/Assets/Scripts/SimpleAI.cs

@@ -0,0 +1,70 @@
+using System.Collections.Generic;
+using UnityEngine;
+
+public class SimpleAI : MonoBehaviour
+{
+    public Unit[] aiUnits;
+    public Flag playerFlag;
+    public Transform aiBase;
+
+    float decisionTimer;
+    const float DecisionInterval = 0.5f;
+    const float RandomOffset = 1.5f;
+
+    void Update()
+    {
+        decisionTimer -= Time.deltaTime;
+        if (decisionTimer <= 0)
+        {
+            MakeDecisions();
+            decisionTimer = DecisionInterval;
+        }
+    }
+
+    void MakeDecisions()
+    {
+        if (playerFlag == null || aiBase == null) return;
+
+        for (int i = 0; i < aiUnits.Length; i++)
+        {
+            var unit = aiUnits[i];
+            if (unit == null || unit.isTaggedOut) continue;
+
+            Vector2 target;
+
+            if (unit.hasFlag)
+            {
+                // Has flag - return to base
+                target = aiBase.position;
+            }
+            else if (playerFlag.carriedBy != null && playerFlag.carriedBy.team == Unit.Team.Enemy)
+            {
+                // Friendly unit has flag - escort or find something else to do
+                // For now, just patrol near own base
+                target = (Vector2)aiBase.position + Random.insideUnitCircle * 5f;
+            }
+            else if (playerFlag.carriedBy != null)
+            {
+                // Player has our flag - chase the carrier
+                target = playerFlag.carriedBy.transform.position;
+            }
+            else
+            {
+                // Flag is at home or dropped - go for it
+                target = playerFlag.transform.position;
+            }
+
+            // Add slight randomness to prevent all units clumping
+            Vector2 randomOffset = Random.insideUnitCircle * RandomOffset;
+
+            // Offset based on unit index for some spread
+            float angle = (i / (float)aiUnits.Length) * Mathf.PI * 2f;
+            Vector2 spreadOffset = new Vector2(Mathf.Cos(angle), Mathf.Sin(angle)) * 1f;
+
+            Vector2 finalTarget = target + randomOffset * 0.5f + spreadOffset;
+
+            // Simple route: straight line to target
+            unit.SetRoute(new List<Vector2> { finalTarget });
+        }
+    }
+}