Finalize 4.1.4 release prep

- BUILD_IMAGE.md: Clarify docs are for devs, not end users
- Add 4.1.5 plan with decode progress bar feature
- Update .gitignore for release assets (.zip, .img)

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

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

PLAN-4.1.5.md

@@ -0,0 +1,106 @@
+# Stegasoo 4.1.5 Plan
+
+## Decode Progress Bar (Real Progress)
+
+Mirror the encode async pattern for decode operations.
+
+### Backend Changes
+
+**1. Add async mode to `/decode` route (`app.py`)**
+- Check for `async=true` form param
+- Generate job_id, store job, submit to executor
+- Return `{"job_id": ..., "status": "pending"}` immediately
+
+**2. Add decode status/progress endpoints (`app.py`)**
+```python
+@app.route("/decode/status/<job_id>")
+def decode_status(job_id):
+    # Return {"status": "pending|running|complete|error", "result": {...}}
+
+@app.route("/decode/progress/<job_id>")
+def decode_progress(job_id):
+    # Read from /tmp/stegasoo_progress_{job_id}.json
+    # Return {"percent": 0-100, "phase": "..."}
+```
+
+**3. Add `_run_decode_job()` background worker (`app.py`)**
+- Similar to `_run_encode_job()`
+- Pass `progress_file` param to decode function
+- Store result/error in job dict
+
+**4. Update decode functions to write progress (`lsb_steganography.py`, `dct_steganography.py`)**
+
+Phases for decode:
+- `"starting"` (0%)
+- `"reading"` (10%) - reading stego image
+- `"extracting"` (30%) - extracting hidden data
+- `"decrypting"` (60%) - Argon2 + AES decryption
+- `"verifying"` (80%) - HMAC verification
+- `"finalizing"` (95%) - preparing output
+- `"complete"` (100%)
+
+### Frontend Changes
+
+**5. Update decode form submission (`decode.html`)**
+- Add async form handler like encode
+- Call `Stegasoo.submitDecodeAsync(form, btn)`
+
+**6. Add decode async methods (`stegasoo.js`)**
+```javascript
+submitDecodeAsync(form, btn)     // POST with async=true, show modal
+pollDecodeProgress(jobId)        // Poll /decode/status, /decode/progress
+```
+
+Reuse existing:
+- `showProgressModal('Decoding')`
+- `updateProgress(percent, phase)`
+
+**7. Handle decode result redirect**
+- On complete: redirect to `/decode/result/{file_id}` or display inline
+
+### Files to Modify
+
+```
+frontends/web/app.py
+  - Add async handling to /decode route (~line 1300+)
+  - Add /decode/status/<job_id> endpoint
+  - Add /decode/progress/<job_id> endpoint
+  - Add _run_decode_job() function
+
+frontends/web/static/js/stegasoo.js
+  - Add submitDecodeAsync()
+  - Add pollDecodeProgress()
+
+frontends/web/templates/decode.html
+  - Update form submit to use async mode
+
+src/stegasoo/lsb_steganography.py
+  - Add progress_file param to decode()
+  - Write progress at each phase
+
+src/stegasoo/dct_steganography.py
+  - Add progress_file param to decode()
+  - Write progress at each phase
+```
+
+### Testing Checklist
+
+- [ ] Decode shows progress modal on submit
+- [ ] Progress bar animates through phases
+- [ ] Successful decode redirects to result
+- [ ] Failed decode shows error in modal
+- [ ] Works for both LSB and DCT modes
+- [ ] Works for message and file payloads
+- [ ] Progress file cleaned up after completion
+
+---
+
+## Other 4.1.5 Ideas (if time)
+
+- [ ] Role-based permissions: admin / mod / user
+- [ ] Better capacity estimates / pre-flight check
+- [ ] Stego detection tool
+
+## Bugs / Nice to Have
+
+- [ ] **flash-stock-img.sh 16GB resize not working** - partition still full SD size after flash, makes dd pull slow. Investigate resize2fs/parted logic and test fix.