export: 32-bit integer and 32-bit float audio; Sample Size lists every size and greys out the unsupported ones

- AudioSettings gains `float`; `bits` takes 16, 24 or 32. `SampleFormat` (Int16 / Int24 /
  Int32 / Float32) and `ExportSettings::supports_sample_format` decide what each codec and
  container stores: WAV, AIFF and QuickTime PCM all four, MXF integers, FLAC integers.
  `validate` refuses float without 32 bits and float in FLAC or MXF.
- WAV float is WAVE_FORMAT_IEEE_FLOAT (EXTENSIBLE for more than two channels) with a `fact`
  chunk; AIFF float is AIFF-C `fl32`; QuickTime float is `lpcm` with the float flag; MXF writes
  32-bit integers. Float keeps the mix as it is, peaks above 0 dBFS included; 16 and 24 bit
  write the same bytes as before.
- FLAC encoder: 8-32 bits. 32-bit stereo is coded independently (a side channel would need 33
  bits), the sample range check no longer overflows, and 32-bit frames point at STREAMINFO for
  the size, which symphonia 0.5 (FilmCraft's own FLAC import) and ffmpeg both read.
- Export mode: Sample Size shows 16 bit, 24 bit, 32 bit and 32 bit float like Audio Format
  does, greying out what the format cannot store with the reason on hover; a size that stops
  being available (float after switching to FLAC) becomes 32-bit integer. es, fr, pt-br, id,
  ja and zh-cn strings.
- Tests: writer layouts and ffprobe codecs for every new format, round trips through ffmpeg
  and FilmCraft's own readers in WAV, AIFF, MOV, MXF and FLAC, headroom of a +6 dB tone,
  refused combinations, full-scale 32-bit FLAC through ffmpeg (MD5 too) and symphonia, and a
  UI test of the selector.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015nzevSsTNZxHPpUngfGTAw

docs/architecture.md

@@ -668,11 +668,11 @@ file.exportMedia {path, preset?, settings?, format?, range?, …}     export.qui
 | `dnxhr` | `filmcraft-dnx` (LB / SQ / HQ / HQX) | MOV (`AVdh`) |
 | `mjpeg` | built in | MOV |
 | `aac` | `filmcraft-aac` (AAC-LC, the audio settings' bitrate) | audio only: MPEG-4 audio `.m4a` (`isobmff`, priming in an edit list), or raw ADTS when the path ends in `.aac` |
-| `mxf-op1a` | DNxHR (default), ProRes or H.264 (Annex B, long GOP), `mxfVideoCodec`; PCM 16/24-bit | MXF OP1a (`filmcraft-mxf` writer: frame-wrapped, index with temporal offsets, start timecode) |
+| `mxf-op1a` | DNxHR (default), ProRes or H.264 (Annex B, long GOP), `mxfVideoCodec`; PCM 16/24/32-bit integer | MXF OP1a (`filmcraft-mxf` writer: frame-wrapped, index with temporal offsets, start timecode) |
 | `mxf-opatom` | as `mxf-op1a` | Avid-style MXF OP-Atom: clip-wrapped picture at `path`, one mono PCM file per channel (`<stem>_A1.mxf` …, `Report::extra_files`) |
 | `png`, `tiff`, `bmp`, `jpg` | `image` | numbered stills `<name>000.<ext>`, `<name>001.<ext>` … |
 | `tga`, `dpx`, `exr` | built in (`raster.rs`: uncompressed Targa 24/32-bit; DPX 10-bit RGB, SMPTE ST 268; OpenEXR half-float linear RGB(A), uncompressed scan lines) | numbered stills, as above |
-| `gif`, `wav`, `aiff` | built in / `image` | GIF / RIFF WAVE (`WAVE_FORMAT_EXTENSIBLE` for 5.1) / AIFF (16- or 24-bit PCM) |
+| `gif`, `wav`, `aiff` | built in / `image` | GIF / RIFF WAVE (`WAVE_FORMAT_EXTENSIBLE` for 5.1; `WAVE_FORMAT_IEEE_FLOAT` + `fact` for float) / AIFF (16-, 24- or 32-bit PCM; 32-bit float as AIFF-C `fl32`) |
 
 - **Reproducible.** The same project and settings give the same file on every machine. Frames render
   in batches of one per core, but the muxer gets them in fixed groups of 16 output frames
@@ -682,7 +682,9 @@ file.exportMedia {path, preset?, settings?, format?, range?, …}     export.qui
 - **Settings.** `ExportSettings` (serde, camelCase, every field optional) holds Video (frame size or
   Match Source, frame rate, Scale to Fit / Fill / Stretch, pixel aspect, field order — progressive
   only, profile / level, bitrate encoding, target / maximum / adaptive bitrate, keyframe distance,
-  maximum render quality), Audio (codec, sample rate, channels, AAC bitrate, PCM sample size),
+  maximum render quality), Audio (codec, sample rate, channels, AAC bitrate, PCM / FLAC sample size: `bits` 16, 24 or 32
+  and `float` for 32-bit float PCM in WAV, AIFF and QuickTime — `supports_sample_format` says
+  which a codec and container store, and Export mode greys out the rest),
   Multiplexer (audio channels: mono, stereo or 5.1, §5.1.1), Captions (burn-in or SRT / WebVTT sidecar), Effects (image / name / timecode
   overlays, video limiter, loudness normalization), Metadata (`udta` `©nam`, `©ART`, `©cpy`, `©des`,
   `©cmt`). `settings.summary()` / `estimate_bytes()` feed Export mode's Summary.