feat: initial release of SplitOverlay (KeyOverlay 1.0.0)

Semi-transparent always-on-top Windows overlay that shows the keymap of a
Vial/QMK split keyboard (Silakka54).

- draws all layers from a Vial .vil layout, transparent keys fall through
- detects the active layer from the keyboard via a Raw HID command (firmware/)
- shows characters of the active Windows input language
- can split the two halves into separate, independently movable windows
- highlights pressed keys; tray menu for opacity, size and options
- Inno Setup installer and portable build; GitHub-style CI workflow

installer/KeyOverlay.iss

@@ -0,0 +1,59 @@
+; Inno Setup script for KeyOverlay. Build with: ISCC.exe /DAppVersion=1.0.0 KeyOverlay.iss
+#ifndef AppVersion
+  #define AppVersion "1.0.0"
+#endif
+
+[Setup]
+AppId={{6F0C2E52-3D1B-4C7E-9B5A-4E8D2A71C9F3}
+AppName=KeyOverlay
+AppVersion={#AppVersion}
+AppPublisher=KeyOverlay
+DefaultDirName={autopf}\KeyOverlay
+DefaultGroupName=KeyOverlay
+DisableProgramGroupPage=yes
+; Per-user install: no administrator rights needed.
+PrivilegesRequired=lowest
+OutputDir=..\dist
+OutputBaseFilename=KeyOverlay-{#AppVersion}-setup
+SetupIconFile=..\src\KeyOverlay\app.ico
+UninstallDisplayIcon={app}\KeyOverlay.exe
+Compression=lzma2/max
+SolidCompression=yes
+ArchitecturesAllowed=x64compatible
+ArchitecturesInstallIn64BitMode=x64compatible
+WizardStyle=modern
+CloseApplications=yes
+AppMutex=Local\KeyOverlay.SingleInstance
+
+[Languages]
+Name: "russian"; MessagesFile: "compiler:Languages\Russian.isl"
+Name: "english"; MessagesFile: "compiler:Default.isl"
+
+[Types]
+Name: "full"; Description: "Полная установка"
+Name: "compact"; Description: "Только KeyOverlay"
+Name: "custom"; Description: "Выборочная установка"; Flags: iscustom
+
+[Components]
+Name: "app"; Description: "KeyOverlay"; Types: full compact custom; Flags: fixed
+Name: "firmware"; Description: "Прошивки для Silakka54 (LEFT / RIGHT, с командой слоя)"; Types: full
+
+[Tasks]
+Name: "desktopicon"; Description: "Ярлык на рабочем столе"; Flags: unchecked
+Name: "autostart"; Description: "Запускать вместе с Windows"; Flags: unchecked
+
+[Files]
+Source: "..\dist\app\KeyOverlay.exe"; DestDir: "{app}"; Components: app; Flags: ignoreversion
+Source: "..\firmware\silakka54_vial_led_keyoverlay_LEFT.uf2"; DestDir: "{app}\firmware"; Components: firmware; Flags: ignoreversion
+Source: "..\firmware\silakka54_vial_led_keyoverlay_RIGHT.uf2"; DestDir: "{app}\firmware"; Components: firmware; Flags: ignoreversion
+Source: "..\firmware\README.md"; DestDir: "{app}\firmware"; Components: firmware; Flags: ignoreversion
+
+[Icons]
+Name: "{autoprograms}\KeyOverlay"; Filename: "{app}\KeyOverlay.exe"
+Name: "{autodesktop}\KeyOverlay"; Filename: "{app}\KeyOverlay.exe"; Tasks: desktopicon
+
+[Registry]
+Root: HKCU; Subkey: "Software\Microsoft\Windows\CurrentVersion\Run"; ValueType: string; ValueName: "KeyOverlay"; ValueData: """{app}\KeyOverlay.exe"""; Flags: uninsdeletevalue; Tasks: autostart
+
+[Run]
+Filename: "{app}\KeyOverlay.exe"; Description: "Запустить KeyOverlay"; Flags: nowait postinstall skipifsilent