fix: preserve gameplay data and correct duel evaluation

- Preserve snake customizations across database migrations and merges.
- Lazily load optional storage backends for SQLite maintenance scripts.
- Match Apex territory and nearest-food tie-breaking semantics.
- Resolve duel occupancy after simultaneous movement and food growth.
- Recompute simulated head-to-head danger after body growth.
- Add regression coverage and declare the aiofiles dependency.

uv.lock

@@ -345,6 +345,7 @@ name = "snake-python"
 version = "0.1.0"
 source = { virtual = "." }
 dependencies = [
+    { name = "aiofiles" },
     { name = "aiologger" },
     { name = "asyncpg" },
     { name = "dotenv" },
@@ -356,6 +357,7 @@ dependencies = [
 
 [package.metadata]
 requires-dist = [
+    { name = "aiofiles", specifier = ">=25.1.0" },
     { name = "aiologger", specifier = ">=0.7.0" },
     { name = "asyncpg", specifier = ">=0.31.0" },
     { name = "dotenv", specifier = ">=0.9.9" },