Add the NX2navi launcher: a one-click setup that builds the game from the player's dump, starts it and keeps it up to date.

NX2navi-Setup.exe installs the launcher into %LOCALAPPDATA%\Programs\NX2navi without administrator rights, with
shortcuts and an Apps entry. The launcher finds the player's .nup, downloads the build tools itself (the MSYS2 UCRT64
packages toolchain.lock.json pins, checked by sha256 and unpacked without pacman, and zbic from PyPI) and runs
tools/make_game.py, whose steps it shows with their progress. Its window follows the game's options menu: colours
sampled from it, the menu's filigree, the white glowing cursor, the Triforce in the title band and as the programs'
icon, and all text in the game's Cetra Display, decoded from the player's own dump. Mouse, keyboard and an XInput
pad drive it.

Updates come from GitHub releases (NX2navi-update.json): the new version is downloaded, checked and staged beside
the running one, the stub restarts into it and falls back to the previous version when it fails to start, and the
game is rebuilt without the dump. make_game.py now keys its exefs and romfs steps on the game files alone, has
--rebuild and --events, compiles only the files whose source, headers, flags or compiler changed, and replaces
ocarina.exe only once the new one links. tools/make_launcher.py builds the release on Windows or Linux.

Tested: tests/launcher_test.py (19 tests), the real toolchain download and install, and under Wine 11 the setup,
the stub, the window on the bundled Windows Python, an update from a local feed by clicking Updates, the rollback
of a version that fails to start, and the downloaded clang compiling and linking a program against the game's
libraries.

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

Merged onto the current port: make_game.py keeps the launcher's step keys, cached link and in-place swap, and its
own runtime manifest (windres), AMD's FidelityFX library and the shader preparation, which becomes a step of its own
("shaders") that the launcher shows in its install, rebuild and update jobs. make_launcher.py ships the shader tools
and, with --ffx, AMD's library.

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

docs/README-BuildKit.md

@@ -4,6 +4,9 @@ This kit builds *The Legend of Zelda: Ocarina of Time* (Nintendo Switch 2, game
 program **on your PC, from your own copy of the game**. The kit contains no game code or data. Everything the build
 writes (`ocarina.exe`, the RomFS image, the shader cache, your saves) comes from your game: keep it to yourself.
 
+The NX2navi launcher (`NX2navi-Setup.exe`, [launcher.md](launcher.md)) does everything below for you, the
+downloads included, and keeps the game up to date. This page is the same build by hand.
+
 ## What you need
 
 - 64-bit Windows 10 or 11, 16 GB of RAM, a Vulkan 1.3 graphics card with mesh shaders and a current driver (tested on