Add per-channel hybrid audio spread spectrum and env feature toggles

Spread spectrum v2: independent per-channel embedding with round-robin
bit distribution, preserving spatial stereo/surround mix. Adaptive chip
tiers (256/512/1024) trade capacity for lossy codec robustness. LFE
channel skipped for 5.1+ layouts. v2 header (20B) with backward-
compatible v0 decode fallback.

Environment toggles (STEGASOO_AUDIO, STEGASOO_VIDEO) gate audio/video
features for minimal builds (e.g. Raspberry Pi image-only). Values:
auto (default, detect deps), 1/true (force on), 0/false (force off).

Web UI fixes: accordion defaults to step 1 on load, chevron arrow
styling, required attribute toggling for audio carrier type switch,
"Images & Mode" renamed to "Reference, Carrier, Mode".

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/stegasoo.1

@@ -1,6 +1,6 @@
 .\" Stegasoo man page
 .\" Generate with: groff -man -Tascii stegasoo.1
-.TH STEGASOO 1 "January 2026" "Stegasoo 4.1.7" "User Commands"
+.TH STEGASOO 1 "February 2026" "Stegasoo 4.3.0" "User Commands"
 .SH NAME
 stegasoo \- steganography with hybrid authentication
 .SH SYNOPSIS
@@ -12,9 +12,10 @@ stegasoo \- steganography with hybrid authentication
 [\fIargs\fR]
 .SH DESCRIPTION
 .B stegasoo
-hides messages and files in images using PIN + passphrase security.
+hides messages and files in images and audio using PIN + passphrase security.
 It uses LSB (Least Significant Bit) steganography with optional DCT
-(Discrete Cosine Transform) encoding for JPEG resilience.
+(Discrete Cosine Transform) encoding for JPEG resilience, and supports
+audio steganography with LSB and Spread Spectrum modes.
 .PP
 Messages are encrypted using a hybrid authentication scheme that combines
 a reference photo (shared secret), passphrase, and PIN code.
@@ -221,6 +222,83 @@ Reset admin password using recovery key.
 .PP
 Options: \fB\-\-db\fR \fIPATH\fR (path to stegasoo.db), \fB\-\-password\fR \fITEXT\fR.
 .RE
+.SS audio\-encode
+Encode a message or file into an audio file.
+.PP
+.B stegasoo audio\-encode
+.I audio
+.B \-r
+.I reference
+[\fB\-m\fR \fImessage\fR | \fB\-f\fR \fIfile\fR]
+[\fIoptions\fR]
+.TP
+.BR \-r ", " \-\-reference " " \fIPATH\fR
+Reference photo (shared secret). Required.
+.TP
+.BR \-m ", " \-\-message " " \fITEXT\fR
+Message to encode.
+.TP
+.BR \-f ", " \-\-file " " \fIPATH\fR
+File to embed instead of message.
+.TP
+.BR \-o ", " \-\-output " " \fIPATH\fR
+Output audio path.
+.TP
+.B \-\-passphrase " " \fITEXT\fR
+Passphrase (recommend 4+ words). Prompts if not provided.
+.TP
+.B \-\-pin " " \fITEXT\fR
+PIN code. Prompts if not provided.
+.TP
+.B \-\-mode " " [\fIlsb\fR|\fIspread\fR]
+Embedding mode: lsb (default) or spread (spread spectrum).
+.PP
+.B Examples:
+.nf
+    stegasoo audio-encode song.wav -r ref.jpg -m "Secret" --passphrase --pin
+    stegasoo audio-encode podcast.mp3 -r ref.jpg -f doc.pdf --mode spread
+.fi
+.SS audio\-decode
+Decode a message or file from a stego audio file.
+.PP
+.B stegasoo audio\-decode
+.I audio
+.B \-r
+.I reference
+[\fIoptions\fR]
+.TP
+.BR \-r ", " \-\-reference " " \fIPATH\fR
+Reference photo (shared secret). Required.
+.TP
+.B \-\-passphrase " " \fITEXT\fR
+Passphrase. Prompts if not provided.
+.TP
+.B \-\-pin " " \fITEXT\fR
+PIN code. Prompts if not provided.
+.TP
+.BR \-o ", " \-\-output " " \fIPATH\fR
+Output path for file payloads.
+.PP
+.B Examples:
+.nf
+    stegasoo audio-decode stego.wav -r ref.jpg --passphrase --pin
+    stegasoo audio-decode stego.wav -r ref.jpg -o ./extracted/
+.fi
+.SS audio\-info
+Display audio file information and steganographic capacity.
+.PP
+.B stegasoo audio\-info
+.I audio
+[\fB\-\-json\fR]
+.PP
+Shows format, sample rate, channels, bit depth, duration, and embedding
+capacity for both LSB and Spread Spectrum modes.
+.PP
+.B Examples:
+.nf
+    stegasoo audio-info song.wav
+    stegasoo audio-info podcast.mp3 --json
+.fi
 .SS tools
 Image security tools.
 .PP