feat: Add integration test suite for v1.1.0 commands

Adds WEEVIL_HOME-based test isolation so cargo test never touches
the real system. All commands run against a fresh TempDir per test.

Environment tests cover doctor, uninstall, new, and setup across
every combination of missing/present dependencies. Project lifecycle
tests cover creation, config persistence, upgrade, and build scripts.

Full round-trip lifecycle test: new → gradlew test → gradlew
compileJava → uninstall → doctor (unhealthy) → setup → doctor
(healthy). Confirms skeleton projects build and pass tests out of
the box, and that uninstall leaves user projects untouched.

34 tests, zero warnings.

src/sdk/mod.rs

@@ -15,15 +15,26 @@ pub struct SdkConfig {
 
 impl SdkConfig {
     pub fn new() -> Result<Self> {
-        let home = dirs::home_dir()
-            .context("Could not determine home directory")?;
+        // Allow tests (or power users) to override the cache directory.
+        // When WEEVIL_HOME is set, we also skip the system Android SDK
+        // search so tests are fully isolated.
+        let (cache_dir, android_sdk_path) = if let Ok(weevil_home) = std::env::var("WEEVIL_HOME") {
+            let cache = PathBuf::from(weevil_home);
+            let android = cache.join("android-sdk");
+            (cache, android)
+        } else {
+            let home = dirs::home_dir()
+                .context("Could not determine home directory")?;
+            let cache = home.join(".weevil");
+            let android = Self::find_android_sdk().unwrap_or_else(|| cache.join("android-sdk"));
+            (cache, android)
+        };
         
-        let cache_dir = home.join(".weevil");
         fs::create_dir_all(&cache_dir)?;
         
         Ok(Self {
             ftc_sdk_path: cache_dir.join("ftc-sdk"),
-            android_sdk_path: Self::find_android_sdk().unwrap_or_else(|| cache_dir.join("android-sdk")),
+            android_sdk_path,
             cache_dir,
         })
     }