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>

scripts/Dockerfile.android-builder

@@ -74,27 +74,6 @@ RUN yes | $ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager --licenses > /dev/nu
         "platform-tools" \
         2>&1 | grep -v '^\[' > /dev/null
 
-# Work around broken API-24 libc/libdl stubs in the NDK. Rust's pre-compiled
-# libstd.rlib for aarch64-linux-android links against pthread_create / dlsym
-# from the sysroot. With --target=...24, those resolve to the API-24 "stub"
-# libc.a/libdl.a that return "libdl.a is a stub --- use libdl.so instead" at
-# runtime. API-26 has real dynamic bindings. Tauri-cli hard-codes the
-# android24-clang path so env var overrides don't stick.
-#
-# Permanent fix inside the image: replace every `${abi}24-clang` binary with
-# a shim that exec()s the corresponding `${abi}26-clang`. Any build using
-# this image now transparently gets the API-26 sysroot even when the caller
-# asks for API-24.
-RUN set -eux; \
-    BIN=$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin; \
-    for abi in aarch64-linux-android armv7a-linux-androideabi i686-linux-android x86_64-linux-android; do \
-        for suffix in clang clang++; do \
-            mv "$BIN/${abi}24-${suffix}" "$BIN/${abi}24-${suffix}.orig"; \
-            printf '#!/bin/sh\nexec "%s/%s26-%s" "$@"\n' "$BIN" "$abi" "$suffix" > "$BIN/${abi}24-${suffix}"; \
-            chmod +x "$BIN/${abi}24-${suffix}"; \
-        done; \
-    done
-
 # Make SDK world-readable so builder user can access it
 RUN chmod -R a+rX $ANDROID_HOME