M1: the tune keeps a beat it sets, instead of one it borrowed

tune.asm counted the screen's frames, because until 6b51d63 the frame
was the only regular beat on the machine. It is now driven by the timer.

THE DURATIONS ARE NOT A CONVERSION OF THE OLD ONES. A frame is 16,667
cycles, so a sixteenth note at 120 beats a minute is seven and a half of
them and could not be asked for at all: the arpeggio was written as
seven whole frames, which is six and a half per cent fast, and the rest
of the piece was written to a tempo picked so its subdivisions landed on
whole frames. The tick is now 125,000 cycles, which IS that sixteenth
note, and the durations are what the music wanted in the first place -
an eighth is two ticks, a quarter four, the arpeggio one each.

The player's loop did not change shape: a note table, a wait on each
beat, the gate dropped at the end. Only what it waits on. The handler
stays a bare RETI, because taking the interrupt is what brings the line
down - a program that POLLED the timer would have to read 0x50, and the
comment now says so, since that is the trap.

Three checks in sound.sh, on a program that is the player's loop rather
than the tune: eight ticks last eight periods to within a tenth of a per
cent, and the seventh and eighth notes are measured where the ticks put
them. The middle one is the one that fails on the old timing - at seven
whole frames the boundary slides under the window and it reads 384 Hz,
which is neither note and is what a crossing counter says when given
two. Verified with break.sh by moving the timer's period a byte.

tune.sbx grew 306 -> 318 bytes, which is why ten cosmos recordings moved:
they quote a directory listing. Nothing else in them changed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Tests/expected/cosmosFault.out

@@ -38,7 +38,7 @@ Crash.sbx               632
 vars.script             50
 blocks.script           343
 loops.script            272
-tune.sbx                306
+tune.sbx                318
 notes.txt               21
 Apps                    <dir>
 hi.script               121