Add 4.1.4 planning doc and release notes

RELEASE_NOTES.md

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+## Stegasoo v4.1.3
+
+### Fixes
+- **SSL Certificate Generation**: First-boot wizard now properly generates self-signed certs when HTTPS is enabled
+- **Download Bug Fixed**: No more "File expired or not found" errors - fixed multi-worker temp file sharing
+- **Docker Build**: Reduced build context from 2.3GB to ~900KB
+
+### Improvements
+- Docker memory limits increased to 2GB (prevents OOM on large DCT operations)
+- Decode button now shows loading spinner during processing
+- Headless Pi flash script with Trixie/NetworkManager support
+
+### Docker
+```bash
+docker-compose up -d web  # Web UI on :5000
+docker-compose up -d api  # REST API on :8000
+```
+
+### Raspberry Pi Image
+Download `stegasoo-rpi-4.1.3.img.zst`, flash to SD card, and boot. The first-boot wizard will guide you through WiFi, HTTPS, and channel key setup.
+
+```bash
+# Flash with included script
+./rpi/flash-image.sh stegasoo-rpi-4.1.3.img.zst /dev/sdX
+
+# First time: save your WiFi credentials
+./rpi/inject-wifi.sh --setup
+
+# Then inject WiFi after flashing
+sudo ./rpi/inject-wifi.sh /dev/sdX
+```
+
+### Full Changelog
+See [CHANGELOG.md](CHANGELOG.md) for complete details.