The surface table said cc 51 moved 533 times somewhere between 1 and 127. That
is a biography, not a state, and it cannot answer the only question you ask a
log at 3am: "why is that orbit silent?". Only the LAST value can.

The data was already in the file — MidiReader.feed() has always coalesced to
count/first/last/min/max per control per second, so `v1` is the value the knob
was left at. The report simply never printed it. This is a formatting change to
capture that already happened.

Three additions:

* `report` gains a `left at` column, and for the three DJ filters it prints what
  that value MEANS in hertz. Transcribing BootTidal.hs:376 turned up something
  worth its own note: for v <= 0.5 the gDJF expression reduces to
  lpf = 180 + 39640*v, i.e. LINEAR IN HERTZ. Pitch perception is logarithmic, so
  that knob spends nearly all its travel in the top two octaves and crosses the
  entire audible bottom in the last ~2% — it feels inert, then collapses. That is
  one gesture producing both "it went quiet" and "it sounds lpf'd", which is
  exactly the pair of symptoms #79 was filed with.

* `gig-log.py controls` — the whole surface, by CC, with each value translated:
  filters to Hz, gMute/gMask to "mutes N% of cycles", panic to armed/clear. It
  ends with an explicit list of anything parked somewhere that silences or thins
  the sound, because a table you have to interpret under stage lights is a table
  you will misread.

* `report --from/--to`, wall clock or +M:SS. The recorder ran 10h48m of which
  ~90 minutes was playing and eight hours was tooling; every aggregate therefore
  described the wrong thing. Windowing has one non-obvious requirement, and it
  gets a test of its own: xrun and throttle are RUNNING TOTALS, so a naive slice
  reports the whole session's count inside the window — wrong, and wrong high.
  slice_session() rebases them to the window.

VALIDATION — it immediately paid for itself by killing two hypotheses:
    49  51  gF1  lpf 16098 Hz — open
    50  59  gF2  lpf 18595 Hz — open
    51  80  gF3  lpf 20000 Hz — open
    41   0  gMask   gates 0% of cycles
    73/74/75 0      mutes 0% of cycles
#79's two leading suspects were "a DJ filter parked below centre" and "a mask
left engaged". Both are now dead, from a file, with no rig and nobody's ears.

83 tests (was 71). The new ones pin the BootTidal arithmetic so it cannot drift
from the Haskell, the last-value ordering rule (latest TIMESTAMP wins, not file
order), the cumulative rebase, and midnight-crossing wall-clock parsing.