v4.1.5: Accordion UI, webcam QR scanning, Pi image fix

Encode/Decode UI:
- New accordion layout with 3 steps (encode) / 2 steps (decode)
- Gold step numbers with checkmarks on completion
- Dynamic right-aligned summaries as fields are filled
- Subtle gradient highlight on active accordion step

Webcam QR Scanning:
- Camera button for RSA key QR codes on encode/decode pages
- Camera button for channel key scanning
- 3-2-1 countdown capture for dense QR codes
- Proper scanner stop/restart on retry
- Backend decompression for STEGASOO-Z: compressed keys

RSA Key Print:
- Removed identifying text from QR print output
- Now prints plain QR code for discretion

Pi Image Script:
- Fixed 16GB resize to detect expand vs shrink
- Fresh images now properly EXPAND to 16GB
- Already-expanded images properly SHRINK to 16GB

UI Polish:
- Removed PIN helper text for compactness
- Fixed QR drop zone centering
- Fixed decode page element IDs for JS

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontends/web/subprocess_stego.py

@@ -314,6 +314,8 @@ class SubprocessStego:
         # Channel key (v4.0.0)
         channel_key: str | None = "auto",
         timeout: int | None = None,
+        # Progress tracking (v4.1.5)
+        progress_file: str | None = None,
     ) -> DecodeResult:
         """
         Decode a message or file from a stego image.
@@ -328,6 +330,7 @@ class SubprocessStego:
             embed_mode: 'auto', 'lsb', or 'dct'
             channel_key: 'auto' (server config), 'none' (public), or explicit key (v4.0.0)
             timeout: Operation timeout in seconds
+            progress_file: Path to write progress updates (v4.1.5)
 
         Returns:
             DecodeResult with message or file_data on success
@@ -340,6 +343,7 @@ class SubprocessStego:
             "pin": pin,
             "embed_mode": embed_mode,
             "channel_key": channel_key,  # v4.0.0
+            "progress_file": progress_file,  # v4.1.5
         }
 
         if rsa_key_data: