Fix HIGH priority issues: unbounded queries, rate limiting, health checks

Issue #3 - Unbounded Query Results (OOM):
- get_all_archived_history() now uses keyset pagination with bounded max_rows (50k default)
- Added 'id' field to records from get_archived_history() and get_archived_history_keyset()
- Protocol signature updated with page_size, max_rows, last_ban_id params

Issue #7 - Docker Health Check Fails:
- Added curl to Dockerfile.backend runtime image
- HEALTHCHECK now uses 'curl -f http://localhost:8000/api/health'
- compose.prod.yml: increased start_period to 40s, timeout to 10s
- Frontend healthcheck proxies to backend /api/health

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Docker/Dockerfile.backend

@@ -33,6 +33,11 @@ FROM docker.io/library/python:3.12-slim AS runtime
 LABEL maintainer="BanGUI" \
       description="BanGUI backend — fail2ban web management API"
 
+# Install curl for healthcheck (used by Docker HEALTHCHECK and Compose healthcheck)
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends curl \
+    && rm -rf /var/lib/apt/lists/*
+
 # Non-root user for security
 RUN groupadd --gid 1000 bangui \
     && useradd --uid 1000 --gid bangui --shell /bin/bash --create-home bangui
@@ -66,8 +71,8 @@ USER bangui
 # Health-check using the built-in health endpoint
 # Returns exit 0 (success) for HTTP 200 (fail2ban online)
 # Returns exit 1 (failure) for HTTP 503 (fail2ban offline)
-HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
-    CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8000/api/health'); print('healthy')" || exit 1
+HEALTHCHECK --interval=30s --timeout=10s --start-period=40s --retries=3 \
+    CMD curl -f http://localhost:8000/api/health || exit 1
 
 # ⚠️  IMPORTANT: Single-Worker Requirement
 # BanGUI must always run as a single worker process: