Only float32 goes to the pedal untouched (fixes #44)

[AliceLafox]

Closes #44.

A beta tester's 16-bit 44.1 kHz stereo WAV was accepted without a word and
the pedal would not play the memory. His 24-bit files worked — and that was
the misleading part: 24-bit DAW exports are WAVE_FORMAT_EXTENSIBLE, which
the gate already refused, so those went through the converter and arrived as
float32. What differed between working and not was conversion, not bit
depth.

The accepted-format set came from rc5cat, which cites Roland's import
documentation for 16/24-bit support. Nobody on our side had measured it.

Measured on hardware

Two empty slots on a real RC-5, identical audio, only the format differing.
Both files landed on the card and neither was rewritten when the pedal left
storage and re-indexed. What the pedal then says about them:

slot 30: name="TEST 16BIT  "  hasAudio=NO   frames=0
slot 31: name="TEST FLOAT32"  hasAudio=YES  frames=529200

The pedal's indexer discards the 16-bit take and accepts the float32 one.

The change

assertUploadable now accepts only float32 — the format the pedal records
in — so everything else takes the converter that already works and that made
the tester's 24-bit files play. pedalAcceptsAsIs simply stops saying yes;
no new code in the import path.

Tests moved with the rule, not around it

• upload validation now expects PCM to be refused
• the import suite gains the reported case: plain 16-bit stereo 44.1 kHz must
  come out float32 with its frame count intact
• command fixtures became float32 — which is what the pedal actually writes —
  and the size arithmetic they carry is now named (frame bytes, source
  header, canonical header) rather than assuming 16-bit geometry

16/16 suites pass.