Termux: build with make, install to $PREFIX, no nl_langinfo on Android

- bootstrap_termux.sh installs pkg-config/binutils, builds with make,
  runs the tests and installs into Termux's $PREFIX/bin.
- Makefile drops -lpthread on Android (pthreads are in bionic libc).
- TUI assumes UTF-8 on Android: nl_langinfo needs API 26, Termux
  targets 24. All sources compile for aarch64-linux-android24 (NDK 27).

scripts/bootstrap_termux.sh

@@ -1,13 +1,12 @@
 #!/data/data/com.termux/files/usr/bin/bash
-# One-shot: clone + build CST-Agent on Android Termux.
+# One-shot: clone, build and install CST-Agent on Android Termux.
 set -euo pipefail
 
 REPO_URL="${CST_AGENT_REPO:-https://git.whcself.xyz/WHC/CST-agent.git}"
 DIR="${1:-CST-agent}"
 
 echo "==> Termux packages"
-pkg install -y git clang make cmake libcurl ncurses-ui-libs 2>/dev/null \
-  || pkg install -y git clang make cmake curl ncurses
+pkg install -y git clang make pkg-config binutils libcurl ncurses
 
 if [[ ! -f "$DIR/Makefile" ]]; then
   echo "==> git clone $REPO_URL -> $DIR"
@@ -15,17 +14,13 @@ if [[ ! -f "$DIR/Makefile" ]]; then
 fi
 cd "$DIR"
 
-echo "==> cmake build (TUI)"
-cmake -B build -DCMAKE_C_COMPILER=clang -DCST_BUILD_TUI=ON
-cmake --build build -j"$(nproc 2>/dev/null || echo 4)"
-# Also keep Makefile binary path convenience
-cp -f build/cst-agent ./cst-agent 2>/dev/null || true
+echo "==> build"
+make -j"$(nproc 2>/dev/null || echo 4)"
+make check || echo "warning: some tests failed (see above)"
+
+echo "==> install to $PREFIX/bin"
+make install
 
 echo
-echo "OK: ./cst-agent  (or ./build/cst-agent)"
-echo "OpenAI-compatible:"
-echo "  export OPENAI_API_KEY=sk-..."
-echo "  export OPENAI_BASE_URL=https://api.openai.com/v1"
-echo "  export OPENAI_MODEL=gpt-4.1-mini"
-echo "  ./cst-agent --workspace \$HOME"
-echo "Docs: docs/env_openai.md"
+echo "OK: run 'cst-agent' inside a project directory."
+echo "The first start asks for the provider and its API key and saves them."