build: default to Release, gate cat-parts to Windows, translate CMake comments

[chiliec]

Three low-risk CMake cleanups from the repo review. No source logic touched.

A. Default CMAKE_BUILD_TYPE to Release when unset

There was no default build type anywhere in the tree. A bare cmake .. — or an IDE that doesn't pass -DCMAKE_BUILD_TYPE — configured the project with empty optimization flags, producing an unoptimized node. Added a standard guard that defaults to Release.

• Guarded on GENERATOR_IS_MULTI_CONFIG, so multi-config generators (MSVC, Ninja Multi-Config) are left alone — they pick the config at build time and are meant to have an empty CMAKE_BUILD_TYPE.
• build-linux.sh and build-mac.sh always pass an explicit type, so their behavior is unchanged; this only affects hand/IDE configures that previously got no optimization.

B. Build cat-parts only on MSVC/MinGW

programs/build_helpers/CMakeLists.txt compiled and linked the cat-parts hardfork concatenator on every platform, but libraries/chain/CMakeLists.txt only invokes it under if(MSVC OR MINGW) — Linux and macOS use cat_parts.py instead. So non-Windows builds were compiling+linking a tool they never run. Wrapped add_executable(cat-parts …) in the same if(MSVC OR MINGW) guard.

Verified the only $<TARGET_FILE:cat-parts> reference lives inside the matching MSVC/MinGW branch; the else() path uses Python and never touches the target, so non-Windows builds are unaffected.

C. Translate leftover Romanian CMake comments

Five comments left over from a prior edit were in Romanian. Translated to English to match the rest of the files:

• CMakeLists.txt — # Păstrăm inițializarea…, # bcrypt trebuie sa fie…
• libraries/chain/CMakeLists.txt — # Target comun…, # Marchează fișierul…, # Variabila folosită…

[On1x]

Folded into the pm branch (our mainnet-bound line, PR #124) to keep the HF14 work consistent and avoid master↔pm divergence. Full CI Docker build on pm is green. Closing here since the change now lives in pm; it'll reach master when pm merges. Thanks!