fix: filter tracing to INFO for wzp crates, WARN for jni crate

The jni crate emits VERBOSE logs for every JNI method lookup (~10 lines
per call, 100+ calls/sec on audio threads). This floods logcat, consumes
CPU, and triggers system kills. Filter to only show INFO+ for our crates
and WARN+ for everything else.

Also fix build script: clean full Rust target to ensure libc++_shared.so
is always copied by cargo-ndk.

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

crates/wzp-android/Cargo.toml

@@ -17,7 +17,7 @@ wzp-crypto = { workspace = true }
 wzp-transport = { workspace = true }
 tokio = { workspace = true }
 tracing = { workspace = true }
-tracing-subscriber = { workspace = true }
+tracing-subscriber = { workspace = true, features = ["env-filter"] }
 bytes = { workspace = true }
 serde = { workspace = true }
 serde_json = "1"