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.

.gitattributes

@@ -34,6 +34,10 @@ Cargo.lock text diff=toml
 *.ico binary
 *.svg text
 
+# Test fixtures
+.gitkeep text
+tests/fixtures/mock-android-sdk/platform-tools/adb binary
+
 # Fonts
 *.ttf binary
 *.otf binary