build(node): bundle dragonx-wallet-rebuild in Linux + Windows releases

Wires the wallet-rebuild recovery helper into the release pipeline so a shipped
build actually carries it (the app locates it next to dragonxd).

- CMakeLists: link the vendored STATIC Berkeley DB for the helper — add
  Threads::Threads + dl (Linux) / ws2_32 (Windows) that the static libdb-6.2 needs
  (the system shared lib pulled those in transitively; the static one doesn't).
- build.sh (Linux + Windows): pass BDB_INCLUDE_DIR/BDB_LIBRARY explicitly at
  configure, pointing at external/dragonx/depends/<triple>/{include,lib/libdb-6.2.a}
  — the same libdb the daemon links, so the helper's output is a v6.2 btree the
  bundled dragonxd reads. Explicit paths bypass find_library (and the mingw
  toolchain's sysroot-only find restriction). Guarded: no depends → helper simply
  not built/bundled. Strip + copy the helper next to dragonxd(.exe) in both bundles.

Verified: Linux links the vendored libdb-6.2.a statically (no dynamic libdb) and
rebuilds the real broken wallet correctly; the helper cross-compiles cleanly with
mingw against the vendored Windows libdb-6.2.a to a PE32+ x64 exe. Full app +
helper build, suite green (1/1), build.sh syntax OK.

Remaining: macOS Berkeley DB (no in-tree depends artifact) + resource-embedding as
an alternative to side-by-side bundling.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CMakeLists.txt

@@ -1089,6 +1089,12 @@ if(BDB_INCLUDE_DIR AND BDB_LIBRARY)
     add_executable(dragonx-wallet-rebuild tools/wallet_rebuild/main.cpp)
     target_include_directories(dragonx-wallet-rebuild PRIVATE ${CMAKE_SOURCE_DIR}/src ${BDB_INCLUDE_DIR})
     target_link_libraries(dragonx-wallet-rebuild PRIVATE ${BDB_LIBRARY})
+    if(WIN32)
+        target_link_libraries(dragonx-wallet-rebuild PRIVATE ws2_32)   # static libdb-6.2 pulls in winsock
+    else()
+        find_package(Threads REQUIRED)
+        target_link_libraries(dragonx-wallet-rebuild PRIVATE Threads::Threads ${CMAKE_DL_LIBS})  # static libdb needs pthread/dl
+    endif()
     set_target_properties(dragonx-wallet-rebuild PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
     message(STATUS "wallet-rebuild helper: ON (Berkeley DB ${BDB_LIBRARY})")
 else()