layout: restructure into src/ tests/ android/ scripts/ tools/

- extension/src/{port,platform,codepage} -> src/; native_render -> src/host
  (+ dxt, shaders/); libgr2 -> src/gr2; extension/third_party -> third_party
- extension/tests -> tests/port, libgr2/tests -> tests/gr2
- android-native -> android (build.sh, push-client.sh moved in)
- script -> scripts; tools/40250 -> tools/server; oracle -> tools/granny-oracle;
  perf tools -> tools/perf
- all build trees under build/ (native, release, android, port-gate)
- xrender:: CMake aliases -> mt::; port-map ledger impl paths rewritten

No code changes. ctest 15/15, port_gate macos+android PASS, port_map check 0 errors.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/py_embed/gen_pyconfig.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 # Generate one platform's pyconfig.h for the vendored CPython 2.7.18 (docs/PORT-PLAN.md 批次 2P step 1).
 # pyconfig.h is the result of probing a platform's type sizes and system calls, so every platform keeps
-# its own copy under extension/third_party/cpython-2.7.18/config/<platform>/. The source list and the
+# its own copy under third_party/cpython-2.7.18/config/<platform>/. The source list and the
 # built-in module table (config/config.c) are shared and only regenerated from the macos run.
 #
 #   tools/py_embed/gen_pyconfig.sh macos|android|ios|linux
@@ -10,7 +10,7 @@
 set -euo pipefail
 cd "$(dirname "$0")/../.."
 REPO="$PWD"
-SRC="$REPO/extension/third_party/cpython-2.7.18"
+SRC="$REPO/third_party/cpython-2.7.18"
 PLAT="${1:?usage: gen_pyconfig.sh macos|android|ios|linux}"
 # config.sub in 2.7.18 predates arm64; the build triple only names the machine running configure.
 BUILD="$(uname -m | sed 's/^arm64$/aarch64/')-$(uname -s | tr 'A-Z' 'a-z')"