fix(env): prevent crash on single-character .env values

A value like `X=a` would pass the startsWith/endsWith quote check
(both `"` and `'` are single chars), then slice(1, -1) would produce
an empty string, silently dropping the value. Add length >= 2 guard
before checking for surrounding quotes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/env.ts

@@ -30,8 +30,9 @@ export function readEnvFile(keys: string[]): Record<string, string> {
     if (!wanted.has(key)) continue;
     let value = trimmed.slice(eqIdx + 1).trim();
     if (
-      (value.startsWith('"') && value.endsWith('"')) ||
-      (value.startsWith("'") && value.endsWith("'"))
+      value.length >= 2 &&
+      ((value.startsWith('"') && value.endsWith('"')) ||
+        (value.startsWith("'") && value.endsWith("'")))
     ) {
       value = value.slice(1, -1);
     }