feat(windows): WireGuard client, auto-VPN, IAM, tray enrichment, installer, CI

Second milestone of the Windows parity work (DESIGN-WINDOWS.md §13).

WireGuard mesh client (signed, WSS-delivered):
- wireguard_apply / wireguard_remove commands: Ed25519-verified, gated on a new
  wireguard capability. Linux applies via wg-quick up/down; Windows installs the
  peer config as a WireGuardTunnel service via wireguard.exe
  (/installtunnelservice, /uninstalltunnelservice)
- state polling in the home monitor drives the blue tray icon and auto-VPN:
  connect when away from home + auto_vpn, disconnect on return (2m cooldown)
- tray VPN toggle and the auto-VPN checkbox are now live; the preference
  persists to agent.yml (PersistAutoVPN)

IAM on Windows (iam_windows.go):
- allowed_login_groups -> net localgroup; ssh_keys -> per-profile
  authorized_keys + %ProgramData%\ssh\administrators_authorized_keys;
  revoke_users -> helper logs off all of the user's WTS sessions;
  sudo_rules logged as no direct equivalent

Tray enrichment:
- Open Config (opens agent.yml), Clear enrollment (re-enroll) menu items
- set_auto_vpn persists; vpn_connect/vpn_disconnect/reinit/open_config commands
  handled by the daemon (tray_server.go)

Packaging & release:
- installer/windows/installer.iss: fully-offline Inno Setup bundle (agent,
  tray, helper, vendor-signed WireGuard MSI, OpenCredential CP, VC++ redist),
  /SILENT /SERVER_URL /JOIN_KEY parameters, SYSTEM service + HKLM Run tray
  autostart, Users-writable %ProgramData%\Theta42 for the IPC socket
- .github/workflows/build-windows.yml: build + test, pinned vendor downloads,
  ISCC compile, Azure Trusted Signing (OIDC), SHA256SUMS, GH release attach,
  optional SSO resource publish
- agent.yml.example documents auto_vpn, wireguard, service_name,
  desktop_helper, public_ip_detect

Tests:
- wireguard_apply/remove dispatch (allowed + capability-denied), PersistAutoVPN,
  ClearEnrollment; dispatch tests pin linuxPlatformOps with a temp WireGuard conf
- end-to-end verified against a local mock SSO on Windows: join-key enrollment
  (token persisted, join key blanked), discovery/telemetry pushed, signed
  arbitrary_bash verified + executed via powershell -EncodedCommand; tray IPC
  socket binds %ProgramData%\Theta42; LDAP byte-pump binds 127.0.0.1:389;
  helper update swap verified

Rebuilds all tracked dist binaries (v2.1.0).

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