v1.2.1

Fixes from a security review, and one step not to undo.

After updating, do not go back to 1.2.0. The first time access from outside
starts, 1.2.1 moves Tailscale's data for this PC from %APPDATA%\PAT Monitor\tsnet
to %LOCALAPPDATA%\PAT Monitor\tsnet. Version 1.2.0 would not find it there and
would register this PC as a new device, with a different public address. If you
have to go back, copy the tsnet folder back first.

Changes you may notice:

• A session signed in on the home network is not accepted through the public
  address. Sign in again when you open the monitor from outside the house. A
  session signed in over Tailscale works on both.
• Talk-back: after two minutes of talking, counting pauses shorter than 30
  seconds, nobody can talk for 30 seconds, so that the room can be heard.
• At most ten viewers at once. The eleventh page says so instead of reporting
  a failed connection.
• Opening the setup or sign-in page on this PC by the computer's name now
  redirects to its address.
• -set-password refuses to run while the monitor is running.

What the monitor now refuses or ignores:

• commands and password submissions that come from pages other than its own;
• a link placed in the recordings folder under a clip's name;
• a link from Tailscale or from the update check that is not a Tailscale page or
  a release page of this project;
• DLLs in the program's own folder: it loads them from Windows' system folder
  only.

Sign-in attempts from one address are checked one at a time, and attempts through
the public address no longer queue ahead of a sign-in at home.

The log writes the public address with the name of your Tailscale network replaced
by <tailnet>, unless the program is started with -v, and a burst of refused
requests is written as one line instead of one line each. Look over a -v log
before attaching it anywhere.

The privacy policy says where
Tailscale's data is kept now.

To update, close the monitor and unpack the zip over the old folder. The zip comes
with a detached signature made with the same key as the previous releases.