Phases 1-7: GUI polish, icons, tray, backups, installer, CI (#1)

* Phase 3: app icon (multi-resolution ICO + master PNG)

scripts/generate-icons.ps1 renders the icon programmatically with
System.Drawing - rounded teal square (#0E7C66) with a stylized white
hook glyph - at 16/24/32/48/64/128/256 px and assembles a proper
multi-resolution Microsoft ICO. The PNG and ICO outputs land in
resources/. The script is the source of truth; re-run after editing
the design.

GUI csproj uses ApplicationIcon for the EXE icon and embeds the .ico
+ .png as Resources so MainWindow and AboutDialog can use them via
WPF's resource URI scheme.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Phase 5: tray icon with minimize-to-tray and context menu

GUI csproj enables UseWindowsForms (NotifyIcon lives in WinForms even
in .NET 8). New Services/TrayIcon.cs wraps NotifyIcon with a context
menu (Open / Restart service / Exit) and the embedded webhook-server
icon. MainWindow creates the TrayIcon, hides itself on minimize and
restores on tray double-click.

Adds GlobalUsings.cs to alias the WPF defaults for types that exist
in both WPF and WinForms (Application, MessageBox, TextBox, Binding,
etc.) so existing code keeps compiling without per-file changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Phase 6+7: Inno Setup installer + GitHub Actions release pipeline

installer/webhook-server.iss is an Inno Setup 6 script that:
- Installs to %ProgramFiles%\WebhookServer
- Creates Start Menu folder + GUI shortcut (and optional desktop icon)
- Runs install-service.ps1 post-install to register the Windows Service
- Runs uninstall-service.ps1 pre-uninstall to remove it
- Bundles the webhook-server icon for the installer / uninstaller

scripts/build-installer.ps1 is the local build helper: publishes both
projects, finds ISCC.exe (PATH or standard install path), compiles the
installer with the version pulled from Directory.Build.props, drops the
output in dist/.

.github/workflows/ci.yml runs build + test on every push/PR to main.
.github/workflows/release.yml triggers on v* tags (or manual dispatch),
runs tests, installs Inno Setup via choco, builds the installer, and
attaches the .exe to a GitHub Release. Pre-1.0 versions are flagged
prerelease automatically.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Phase 4: backups + import/export config

ConfigStore.SaveAsync now snapshots the previous config to
%ProgramData%\WebhookServer\backups\config-<timestamp>.json before
overwriting, retaining the last 30. Failures are silent so a
backup-write hiccup never blocks an actual save.

Three new admin pipe ops:
- list-backups: returns newest 50 entries with timestamps and sizes
- restore-backup: takes a fileName, refuses path-traversal chars,
  loads the named backup over the live config (which itself triggers
  a fresh backup of the current state via the SaveAsync hook)
- import-config: replaces the current config with a GUI-supplied
  ServerConfig, merging encrypted secrets where the GUI didn't supply
  new plaintext

GUI File menu items are wired:
- Import config: file picker -> ImportConfigAsync
- Export config: SaveFileDialog writes the current config as JSON
- Backups: dynamic submenu auto-refreshed when opened, listing
  backups with timestamp + size; click to confirm-and-restore

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/WebhookServer.Core/Ipc/AdminProtocol.cs

@@ -23,6 +23,21 @@ public static class AdminOps
     public const string BindHttps = "bind-https";
     public const string RestartListener = "restart-listener";
     public const string Ping = "ping";
+    public const string ListBackups = "list-backups";
+    public const string RestoreBackup = "restore-backup";
+    public const string ImportConfig = "import-config";
+}
+
+public sealed class BackupEntry
+{
+    public string FileName { get; set; } = "";
+    public DateTimeOffset SavedAt { get; set; }
+    public long SizeBytes { get; set; }
+}
+
+public sealed class RestoreBackupArgs
+{
+    public string FileName { get; set; } = "";
 }
 
 public sealed class AdminRequest