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/oracle_diff/main.cpp

@@ -1,4 +1,4 @@
-// oracle_diff —— libgr2 vs oracle 逐字段对拍（M2 门禁·主）。见 oracle/FORMAT.md、docs/steps/00-oracle.md
+// oracle_diff —— libgr2 vs oracle 逐字段对拍（M2 门禁·主）。见 tools/granny-oracle/FORMAT.md、docs/steps/00-oracle.md
 //
 //   oracle_diff <model.gr2> [<anim.gr2>|-] <oracle_dump.bin> [--t <sec>] [--mesh N]
 //