Return an AIFF input as WAV and reword the interface text

HARP accepts .aif, the extension Logic Pro gives AIFF, but soundfile cannot write a file named with it, so such an input failed when its result was written. Gradio also converts an AIFF output to 16-bit WAV, since browsers cannot play AIFF, so keeping that container gained nothing. Lossless inputs now keep WAV and FLAC alone, and AIFF comes back as WAV at the bit depth this Space writes.

Some of the description and help text joined clauses with a semicolon or ended a sentence with a preposition, and each such sentence is reworded.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app.py

@@ -23,7 +23,7 @@ model_card = ModelCard(
     description=(
         "Background noise suppression / speech enhancement using "
         "DeepFilterNet3. Slider controls strength through wet/dry blend. Denoising runs at "
-        "48 kHz in mono; the result is resampled back to the input's rate and copied across its "
+        "48 kHz in mono. The result is resampled back to the input's rate and copied across its "
         "channels, so the output matches the format it came in with but carries "
         "no stereo image. Repository: https://github.com/Rikorose/DeepFilterNet "
         "Paper: https://arxiv.org/abs/2305.08227"
@@ -34,7 +34,7 @@ model_card = ModelCard(
 
 # A lossless input keeps its container. A lossy one comes back as WAV, since encoding the result
 # lossily again would expose the artifacts of the first encode and add a second set.
-LOSSLESS = {".wav", ".flac", ".aiff", ".aif"}
+LOSSLESS = {".wav", ".flac"}
 
 # -----------------------------
 # Device & Model Initialization