Add Windows installer via Inno Setup

New packaging/windows/orbithub.iss packages the build directory's
top-level contents directly (orbithub.exe, *.dll, platforms/,
sqldrivers/) rather than going through cmake --install: vcpkg's own
applocal DLL deployment already drops every required runtime dependency
flat into build/ on every build (confirmed repeatedly this session), and
the existing private-runtime-lib install() rule uses an RPATH-style Unix
convention (lib/orbithub/) that doesn't work on Windows, where DLLs must
sit next to the exe. Produces a single OrbitHub-Setup-<version>.exe with
a Start Menu entry, optional desktop shortcut, and uninstaller.

build-installer.ps1 reads the project version from build/CMakeCache.txt
(same approach build-deb.sh already uses) and drives ISCC.exe.

Code signing is out of scope for now (no certificate available), so the
installer will trigger a SmartScreen warning until one is purchased.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packaging/windows/orbithub.iss

@@ -0,0 +1,46 @@
+#ifndef MyAppVersion
+#define MyAppVersion "0.0.0"
+#endif
+
+#define MyAppName "OrbitHub"
+#define MyAppPublisher "OrbitHub Maintainers"
+#define MyAppExeName "orbithub.exe"
+#define MyBuildDir "..\..\build"
+
+[Setup]
+AppId={{6B2E0B8F-2C6D-4E7C-9C36-6C6C9C6F6C1A}
+AppName={#MyAppName}
+AppVersion={#MyAppVersion}
+AppPublisher={#MyAppPublisher}
+DefaultDirName={autopf}\{#MyAppName}
+DefaultGroupName={#MyAppName}
+UninstallDisplayIcon={app}\{#MyAppExeName}
+OutputDir=..\..\dist\windows
+OutputBaseFilename=OrbitHub-Setup-{#MyAppVersion}
+Compression=lzma2
+SolidCompression=yes
+ArchitecturesAllowed=x64compatible
+ArchitecturesInstallIn64BitMode=x64compatible
+SetupIconFile=orbithub.ico
+WizardStyle=modern
+DisableProgramGroupPage=yes
+
+[Languages]
+Name: "english"; MessagesFile: "compiler:Default.isl"
+
+[Tasks]
+Name: "desktopicon"; Description: "Create a &desktop shortcut"; GroupDescription: "Additional icons:"; Flags: unchecked
+
+[Files]
+Source: "{#MyBuildDir}\{#MyAppExeName}"; DestDir: "{app}"; Flags: ignoreversion
+Source: "{#MyBuildDir}\*.dll"; DestDir: "{app}"; Flags: ignoreversion
+Source: "{#MyBuildDir}\platforms\*"; DestDir: "{app}\platforms"; Flags: ignoreversion recursesubdirs
+Source: "{#MyBuildDir}\sqldrivers\*"; DestDir: "{app}\sqldrivers"; Flags: ignoreversion recursesubdirs
+
+[Icons]
+Name: "{group}\{#MyAppName}"; Filename: "{app}\{#MyAppExeName}"
+Name: "{group}\Uninstall {#MyAppName}"; Filename: "{uninstallexe}"
+Name: "{autodesktop}\{#MyAppName}"; Filename: "{app}\{#MyAppExeName}"; Tasks: desktopicon
+
+[Run]
+Filename: "{app}\{#MyAppExeName}"; Description: "Launch {#MyAppName}"; Flags: nowait postinstall skipifsilent