Initial production-ready Gemma 3 vLLM ROCm stack

Co-Authored-By: Oz <oz-agent@warp.dev>

docs/UPGRADE_NOTES.md

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+# Upgrade Notes
+## Standard safe upgrade path
+From repository root:
+```bash
+git pull
+docker compose pull
+./scripts/restart.sh
+```
+Then run smoke tests:
+```bash
+./scripts/test_api.sh
+./scripts/test_ui.sh
+python3 scripts/test_python_client.py
+```
+
+## Versioning guidance
+- Prefer pinning image tags in `docker-compose.yml` once your deployment is stable.
+- Upgrading vLLM may change runtime defaults or engine behavior; check vLLM release notes before major version jumps.
+- Keep `GEMMA_MODEL_ID` explicit in `.env` to avoid unintentional model drift.
+
+## Model upgrade considerations
+When changing Gemma 3 variants (for example, from 1B to larger sizes):
+- Verify host RAM and GPU memory capacity.
+- Expect re-download of model weights and larger disk usage.
+- Re-tune:
+  - `VLLM_MAX_MODEL_LEN`
+  - `VLLM_GPU_MEMORY_UTILIZATION`
+- Re-run validation scripts after restart.
+
+## Backup recommendations
+Before major upgrades, back up local persistent data:
+```bash
+mkdir -p backups
+tar -czf backups/hf-cache-$(date +%Y%m%d-%H%M%S).tar.gz "${HOME}/.cache/huggingface"
+tar -czf backups/open-webui-data-$(date +%Y%m%d-%H%M%S).tar.gz frontend/data/open-webui
+```
+If you use local predownloaded models:
+```bash
+tar -czf backups/models-$(date +%Y%m%d-%H%M%S).tar.gz models
+```
+
+## Rollback approach
+If a new image/model combination fails:
+1. Revert `docker-compose.yml` and `.env` to previous known-good values.
+2. Pull previous pinned images (if pinned by tag/digest).
+3. Restart:
+```bash
+./scripts/restart.sh
+```
+4. Re-run smoke tests.