Run a dictation and a command to the agent at the same time

The two shared one state machine, which meant an agent thinking for a minute
was a minute in which nothing could be dictated. That is the wrong trade: the
work has nothing in common past the microphone, and the microphone is busy for
the seconds you are speaking, not the minute afterwards.

So they are two flows now, each with its own state, its own pipeline and its own
indicator. Either can be working while the other records. Only the recorder is
taken in turns, because there is one of it: whichever asks second is refused
while the first holds it, and the menu entry greys out to say so rather than
failing quietly. "Am I recording" is read off the two states rather than off the
recorder's owner, which outlives the recording by the moment it takes the audio
to arrive, and would otherwise report a microphone as busy after it was free.

Two indicators in one corner would sit on top of each other, so an indicator can
be told what it stacks on: it offsets by that one's height while it is showing
and drops back into the corner when it goes, which the animation timer notices
without anything having to tell it.

Pasting is now under a lock. It is three steps rather than one, read the
clipboard, write ours, press the key, and two runs finishing together would
paste one answer and restore the other's clipboard over it.

Calling off the agent is its own menu entry and its own command, instead of a
cancel that meant different things depending on what was running. The tray icon
still ends whichever recording is going.

README.md

@@ -55,6 +55,9 @@ set next to it.
 An indicator in the screen corner shows a red dot, a live waveform and the
 elapsed time, then the stage it is on. It never takes focus. Pressing
 `Ctrl+Space` again while Dikte is still working does nothing; nothing queues up.
+A dictation and a command to the agent do wait on each other for the microphone,
+which is one device, but for nothing else: each has its own indicator, and the
+second one stacks above the first while both are up.
 
 ## What it does