docs: add production deployment example with volumes and .env

- docker/docker-compose.prod.yml: pulls image from 192.168.0.19:5000,
  mounts config/, wiki/ and db/ as separate volumes, health check, TZ support
- .env.example: fully commented template for all env vars
- .gitignore: ignore .env, always track .env.example
- README: deployment section with step-by-step guide, volume table, backup commands
- config.go: default db_path to /data/db/archivum.db (matches prod volume layout)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/docker-compose.prod.yml

@@ -0,0 +1,81 @@
+# ── Production deployment example ─────────────────────────────────────────────
+#
+# Uses the pre-built image from your private registry.
+# Copy this file to your server and run:
+#
+#   docker compose -f docker-compose.prod.yml up -d
+#
+# Prerequisites on the host:
+#   - Create the directories listed under "volumes" (or adjust paths in .env)
+#   - Populate config/config.json (see README for the JSON schema)
+#     OR leave it empty and the Setup Wizard will create it on first access.
+#
+# ── Directory layout this file expects ────────────────────────────────────────
+#
+#   /opt/archivum/          (or whatever ARCHIVUM_BASE points to)
+#   ├── config/
+#   │   └── config.json     ← backend configuration (auto-created by wizard)
+#   ├── wiki/               ← AsciiDoc source files (git repo lives here)
+#   └── db/
+#       └── archivum.db     ← SQLite database (auto-created on first start)
+#
+# ── Quick start ────────────────────────────────────────────────────────────────
+#   cp .env.example .env    # edit to match your environment
+#   mkdir -p /opt/archivum/{config,wiki,db}
+#   docker compose -f docker-compose.prod.yml pull
+#   docker compose -f docker-compose.prod.yml up -d
+# ──────────────────────────────────────────────────────────────────────────────
+
+services:
+  archivum:
+    image: ${REGISTRY:-192.168.0.19:5000}/archivum:${IMAGE_TAG:-latest}
+    container_name: archivum
+    restart: unless-stopped
+
+    ports:
+      - "${HOST_PORT:-8080}:4000"
+
+    environment:
+      # Path inside the container where config.json is looked up.
+      DOCKER_PATH: /config
+
+      # Path inside the container where the Vue SPA is served from.
+      # Change only if you override the Dockerfile.
+      UI_DIR: /srv/archivum/ui
+
+      # Match the UID/GID of the user that owns the host directories.
+      PUID: ${PUID:-1000}
+      PGID: ${PGID:-1000}
+
+      # Optional: set TZ for correct git commit timestamps.
+      TZ: ${TZ:-Europe/Stockholm}
+
+    volumes:
+      # ── Configuration ──────────────────────────────────────────────────────
+      # config.json (backend) and settings.json (frontend) live here.
+      # The Setup Wizard writes config.json here on first run.
+      - ${ARCHIVUM_CONFIG:-/opt/archivum/config}:/config
+
+      # ── Wiki files (AsciiDoc source + git repo) ────────────────────────────
+      # This directory becomes the git repository root.
+      # Map it to wherever you want the .adoc files to live on the host.
+      - ${ARCHIVUM_WIKI:-/opt/archivum/wiki}:/data/wiki
+
+      # ── SQLite database ────────────────────────────────────────────────────
+      # Mounting the db directory separately makes it easy to back up the
+      # database independently of the wiki content.
+      - ${ARCHIVUM_DB:-/opt/archivum/db}:/data/db
+
+    # Optional: limit resource usage on a Raspberry Pi 5.
+    # deploy:
+    #   resources:
+    #     limits:
+    #       cpus: "2.0"
+    #       memory: 512M
+
+    healthcheck:
+      test: ["CMD", "wget", "-qO-", "http://localhost:4000/health"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 10s