v1.0-build180 — named server sets + security hardening

Named servers (builds 173-180)

• Settings now holds a list of named servers with one active at a time:
  tap the circle to make a server active, tap its name to edit it.
• Each server carries its own transport mode, proxy / TURN addresses,
  WireGuard keys and connection settings. The VK call link and VK account
  auth stay global and are shared by every server.
• New / Copy / Delete in the server editor; the last remaining server
  cannot be deleted. Your existing configuration migrates to "Server1"
  on first launch, so nothing changes until you add a second server.
• The main screen shows which server you are connected to, and the log
  records the active server on launch, on switch and on connect.
• Full Backup now stores every server plus the active one. Backups from
  build 178 and earlier still import — they restore as a single "Server1".
  Note that a backup exported by this build is NOT readable by older builds.
• Importing a connection link (vkturnproxy:// / freeturn:// / wdtt://) now
  ADDS a server and makes it active instead of overwriting your settings;
  existing servers are kept. A freeturn:// server starts without WireGuard
  keys — enter them in the editor.
• quick_link.py emits serverName and can build a link from the new backup
  format, including --server to pick a specific server.

Security hardening (build 172)

• Reject control characters in an imported allowedIPs / peerAddress before
  they reach the WireGuard UAPI config, which could otherwise smuggle extra
  directives such as a hidden second peer.
• Validate the SRTP-WRAP-A provisioning address; a malformed one crashed
  the tunnel extension on every connect.
• Bound the VK captcha slider grid size taken from the server response,
  which could otherwise force a multi-gigabyte allocation.
• Sanitize the Wi-Fi SSID before it is written to the shared log, so a
  crafted network name cannot forge log lines.
• Reject non-finite expiry values in the cached TURN credentials, which
  could crash the app on every connect after a tampered backup.