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>

PLAN-4.1.5.md

@@ -95,6 +95,47 @@ src/stegasoo/dct_steganography.py
 
 ---
 
+---
+
+## Browser Webcam QR Scanning
+
+Add webcam-based QR code scanning for all key input fields.
+
+### Use Cases
+- Import channel key via QR scan on account page
+- Scan QR codes instead of typing long keys
+
+### Implementation
+
+**1. Add JS QR scanning library**
+- Use `jsQR` or `html5-qrcode` (client-side, no server needed)
+- Include via CDN in base template
+
+**2. Add camera button to channel key inputs**
+- Account page: "Add Key" field
+- Encode/decode pages: channel key selector (if manual input)
+
+**3. Camera modal component**
+- Request camera permission
+- Live video preview
+- Auto-detect QR and populate input field
+- Close modal on successful scan
+
+### Files to Modify
+```
+frontends/web/templates/base.html      - Add QR library CDN
+frontends/web/templates/account.html   - Camera button + modal
+frontends/web/static/js/stegasoo.js    - QR scan methods
+```
+
+### Testing Checklist
+- [ ] Camera permission prompt works
+- [ ] QR detected and input populated
+- [ ] Works on mobile browsers
+- [ ] Graceful fallback if no camera
+
+---
+
 ## Other 4.1.5 Ideas (if time)
 
 - [ ] Role-based permissions: admin / mod / user