Add Windows installer (Inno Setup) + GUI-subsystem release builds

Package PeerSpeak for Windows as a single self-contained binary. The GUI
icon, notification chimes, and avatar presets are already embedded via
include_bytes!, and the cross-compiled .exe is statically linked (no extra
DLLs), so the installer payload is just peerspeak.exe plus an .ico.

- src/main.rs: set windows_subsystem = "windows" for release builds so the
  GUI launches without a stray console window (debug keeps the console for
  stderr/panics).
- packaging/windows/: Inno Setup script (peerspeak.iss), multi-resolution
  app icon (peerspeak.ico), and a build README. The installer drops a
  Start-menu/desktop shortcut, optionally adds a Windows Firewall allow-rule
  (iroh UDP hole-punching), and provides an uninstaller.
- win-cross-build.sh: promote the cross-build helper from a throwaway to the
  documented installer build step; .gitignore the staged exe + compiled
  setup.exe build artifacts.

Built with Inno Setup 6.7.1 under Wine; binary is unsigned (SmartScreen will
warn until code-signed).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packaging/windows/README.md

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+# PeerSpeak — Windows installer
+
+This directory builds a Windows setup installer for PeerSpeak using
+[Inno Setup](https://jrsoftware.org/isinfo.php).
+
+PeerSpeak ships as a **single self-contained `peerspeak.exe`** — the GUI icon,
+notification chimes, and avatar presets are all embedded in the binary
+(`include_bytes!`), and the executable is statically linked against the GNU
+runtime, so there are no extra DLLs to bundle. The installer payload is just the
+`.exe` plus an `.ico` for the Start-menu / desktop shortcuts.
+
+## Files
+
+| File | Tracked | Purpose |
+|------|---------|---------|
+| `peerspeak.iss` | yes | Inno Setup script |
+| `peerspeak.ico` | yes | multi-resolution app icon (from `assets/icons/*.png`) |
+| `README.md` | yes | this file |
+| `peerspeak.exe` | no (gitignored) | staged build artifact, copied from `target/x86_64-pc-windows-gnu/release/` |
+| `output/peerspeak-<ver>-setup.exe` | no (gitignored) | the compiled installer |
+
+## Build steps
+
+1. **Cross-compile the Windows binary** (from the repo root, inside the
+   `peerspeak-win` archlinux distrobox):
+
+   ```sh
+   RUSTC_BOOTSTRAP=1 ./win-cross-build.sh -Z build-std=std,panic_abort
+   ```
+
+   This needs the `rust-src` component and the `x86_64-pc-windows-gnu` target
+   installed in that toolchain. The result is a statically-linked,
+   GUI-subsystem `.exe` (no stray console window).
+
+2. **Stage the binary** next to the script:
+
+   ```sh
+   cp target/x86_64-pc-windows-gnu/release/peerspeak.exe packaging/windows/
+   ```
+
+3. **Regenerate the icon** if the source PNGs changed:
+
+   ```sh
+   magick assets/icons/peerspeak-16.png assets/icons/peerspeak-24.png \
+          assets/icons/peerspeak-32.png assets/icons/peerspeak-48.png \
+          assets/icons/peerspeak-64.png assets/icons/peerspeak-128.png \
+          assets/icons/peerspeak-256.png packaging/windows/peerspeak.ico
+   ```
+
+4. **Compile the installer** with Inno Setup. On Linux this runs under Wine:
+
+   ```sh
+   cd packaging/windows
+   wine ~/.wine/drive_c/InnoSetup6/ISCC.exe peerspeak.iss
+   ```
+
+   The installer lands at `output/peerspeak-<version>-setup.exe`.
+
+## What the installer does
+
+- Installs `peerspeak.exe` to `Program Files\PeerSpeak` (requires admin / one
+  UAC prompt).
+- Creates a Start-menu shortcut, with an optional desktop shortcut.
+- Optionally adds a Windows Firewall allow-rule for PeerSpeak (recommended —
+  iroh uses UDP hole-punching, so this avoids a mid-call firewall prompt). The
+  rule is removed on uninstall.
+- Provides a standard uninstaller.
+
+> **Note:** the installer and the binary are **not code-signed**, so Windows
+> SmartScreen will show an "unknown publisher" warning on first run. The user
+> clicks *More info → Run anyway*. Removing this warning requires a paid
+> code-signing certificate.

packaging/windows/peerspeak.iss

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+; Inno Setup script for PeerSpeak (Windows installer).
+;
+; PeerSpeak is a single self-contained binary: the GUI icon, notification
+; chimes, and avatar presets are all embedded in the .exe (include_bytes!),
+; so the only payload here is peerspeak.exe plus an .ico for the shortcuts.
+;
+; Build (under Wine on Linux, or native Windows):
+;   wine "C:\Program Files (x86)\Inno Setup 6\ISCC.exe" peerspeak.iss
+; Output lands in .\output\peerspeak-<version>-setup.exe
+;
+; The peerspeak.exe is cross-compiled with win-cross-build.sh
+; (x86_64-pc-windows-gnu, statically linked -- no extra DLLs needed).
+
+#define MyAppName "PeerSpeak"
+#define MyAppVersion "0.2.0"
+#define MyAppPublisher "mollusk"
+#define MyAppExeName "peerspeak.exe"
+
+[Setup]
+; A stable AppId keeps upgrades/uninstall tracking consistent across versions.
+AppId={{2754D6C1-C8A4-4B13-9824-2D303439739D}
+AppName={#MyAppName}
+AppVersion={#MyAppVersion}
+AppVerName={#MyAppName} {#MyAppVersion}
+AppPublisher={#MyAppPublisher}
+DefaultDirName={autopf}\{#MyAppName}
+DefaultGroupName={#MyAppName}
+DisableProgramGroupPage=yes
+UninstallDisplayIcon={app}\{#MyAppExeName}
+SetupIconFile=peerspeak.ico
+Compression=lzma2/max
+SolidCompression=yes
+WizardStyle=modern
+OutputDir=output
+OutputBaseFilename=peerspeak-{#MyAppVersion}-setup
+; Program Files install + firewall rule both need elevation.
+PrivilegesRequired=admin
+ArchitecturesAllowed=x64compatible
+ArchitecturesInstallIn64BitMode=x64compatible
+
+[Languages]
+Name: "english"; MessagesFile: "compiler:Default.isl"
+
+[Tasks]
+Name: "desktopicon"; Description: "{cm:CreateDesktopIcon}"; GroupDescription: "{cm:AdditionalIcons}"; Flags: unchecked
+Name: "firewall"; Description: "Allow PeerSpeak through Windows Firewall (recommended for voice calls)"; GroupDescription: "Network:"
+
+[Files]
+Source: "peerspeak.exe"; DestDir: "{app}"; Flags: ignoreversion
+Source: "peerspeak.ico"; DestDir: "{app}"; Flags: ignoreversion
+
+[Icons]
+Name: "{group}\{#MyAppName}"; Filename: "{app}\{#MyAppExeName}"; IconFilename: "{app}\peerspeak.ico"
+Name: "{group}\{cm:UninstallProgram,{#MyAppName}}"; Filename: "{uninstallexe}"
+Name: "{autodesktop}\{#MyAppName}"; Filename: "{app}\{#MyAppExeName}"; IconFilename: "{app}\peerspeak.ico"; Tasks: desktopicon
+
+[Run]
+; iroh uses UDP hole-punching; pre-authorizing avoids a mid-call firewall prompt.
+Filename: "{sys}\netsh.exe"; Parameters: "advfirewall firewall add rule name=""PeerSpeak"" dir=in action=allow program=""{app}\{#MyAppExeName}"" enable=yes profile=any"; Flags: runhidden; Tasks: firewall
+Filename: "{app}\{#MyAppExeName}"; Description: "{cm:LaunchProgram,{#MyAppName}}"; Flags: nowait postinstall skipifsilent
+
+[UninstallRun]
+Filename: "{sys}\netsh.exe"; Parameters: "advfirewall firewall delete rule name=""PeerSpeak"""; Flags: runhidden; RunOnceId: "DelPeerSpeakFirewall"