revert(android): roll back to build #6 (35642d1) — pre-oboe known-good state

Spent 10+ builds chasing a __init_tcb+4 / pthread_create SIGSEGV after
adding the oboe audio backend. Every "fix" made things worse. Reverting
all Android-specific files to the state at 35642d1 (build #6), which
was the last commit where the Tauri Android app actually launched,
rendered the home screen, and successfully registered on a relay.

Reverted files (all back to their 35642d1 content):
  - desktop/src-tauri/Cargo.toml        (no build-dep cc, no tracing-android)
  - desktop/src-tauri/build.rs          (git hash only, no Oboe / cc build)
  - desktop/src-tauri/src/lib.rs        (engine cfg-gated on non-android)
  - desktop/src-tauri/src/main.rs       (two-line desktop entry)
  - desktop/src-tauri/src/engine.rs     (desktop-only audio setup)
  - scripts/Dockerfile.android-builder  (no android24→26 clang shim)
  - scripts/build-tauri-android.sh      (no linker env vars / manifest patch)

Deleted (were added between b314138 and e2e023d):
  - desktop/src-tauri/cpp/getauxval_fix.c
  - desktop/src-tauri/cpp/oboe_bridge.{h,cpp}
  - desktop/src-tauri/cpp/oboe_stub.cpp
  - desktop/src-tauri/src/oboe_audio.rs

Next: rebuild image on remote (to drop the baked-in clang shim), build
an APK, install on Pixel 6, verify the UI renders the same way build #6
did. From there we add features back ONE at a time so we can actually
bisect which one triggers the tao::ndk_glue crash. User's rule:
"if you want to change stack, change incrementally, so we can debug".

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

desktop/src-tauri/cpp/oboe_stub.cpp

@@ -1,27 +0,0 @@
-// Stub implementation for non-Android host builds (testing, cargo check, etc.)
-
-#include "oboe_bridge.h"
-#include <stdio.h>
-
-int wzp_oboe_start(const WzpOboeConfig* config, const WzpOboeRings* rings) {
-    (void)config;
-    (void)rings;
-    fprintf(stderr, "wzp_oboe_start: stub (not on Android)\n");
-    return 0;
-}
-
-void wzp_oboe_stop(void) {
-    fprintf(stderr, "wzp_oboe_stop: stub (not on Android)\n");
-}
-
-float wzp_oboe_capture_latency_ms(void) {
-    return 0.0f;
-}
-
-float wzp_oboe_playout_latency_ms(void) {
-    return 0.0f;
-}
-
-int wzp_oboe_is_running(void) {
-    return 0;
-}