Pause / 'Freeze game state' button

[zaroth]

Somewhat similar to #332. It would be nice to have an equivalent of shouting "WAIT!" in real life. Both players should have the ability to freeze/unfreeze on will - it's just to prevent the other player from going through a sequence when we have ability to interfere. Possible uses:

1. Mistakenly making/continuing a run. Currently the way to fix it is to jack out before the opponent has a chance to rez/react, but as #1343 points out, it's wrong from the mechanical point of view.
2. "Install, Advance, Advance, Score". Clicking a hovered Pause button is faster than clone chipping a Clot.
3. Using Shards, such as Utopia Shard after SEA Source, but before 2 Scorches.
4. Councilman. Enough said.

The idea could be even further improved upon by adding some QoL changes, such as:

• allowing players to specify triggers when the game should auto-freeze from their PoV, similar to watch conditions/breakpoints in debuggers. Ranging from simple, such as before opponents ends their turn (which would incidentally help #696) or after opponent spends a click to more specific, such as after opponent advances a card or maybe even after opponent advances THIS card.
• default pause off countdown, e.g. 5 seconds - since this is not a real time game, the freeze is meant primarily as a signal to explain things to the opponent, not a full stop
• some sort of visual cue the game is paused, e.g. greying out the whole game area except the Unpause button and the chat/game log.

[queueseven]

Maybe we could have something like in Shandalar:

Here you can see a bar with all the game phases. You can click on a phase to set a break point, and the game will stop to let you react when the phase is reached. Some phases (like the upkeed- and mainphase stop the game by default).