fix: container permissions and volume setup

Problems fixed:
- archivum user (UID 1000) could not write to bind-mounted /config or /data
  because Docker (especially on Windows/WSL2) creates volumes owned by root
- /data/wiki and /data/db subdirectories were never created, causing
  "no such file or directory" when the app tried to write files

Changes:
- docker/entrypoint.sh: runs as root, creates /config /data/wiki /data/db,
  chowns them to PUID:PGID, then drops privileges via su-exec
- Dockerfile: install su-exec + git, copy entrypoint, remove build-time
  USER directive (privilege drop happens at runtime via entrypoint)
- docker-compose.yml: switch local dev to named volumes so Docker manages
  ownership automatically (avoids Windows/WSL2 bind-mount permission issues);
  add TZ env var; explicit comments on how to switch to bind mounts

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

docker/entrypoint.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+# Archivum container entrypoint
+# Runs as root, creates directories, fixes permissions, then drops to PUID:PGID.
+set -e
+
+PUID="${PUID:-1000}"
+PGID="${PGID:-1000}"
+
+echo "[entrypoint] starting as uid=$(id -u) gid=$(id -g)"
+echo "[entrypoint] target PUID=${PUID} PGID=${PGID}"
+
+# ── Ensure required directories exist ──────────────────────────────────────
+mkdir -p /config
+mkdir -p /data/wiki
+mkdir -p /data/db
+
+# ── Fix ownership so the app user can read/write all volumes ───────────────
+# This is needed because:
+#   - bind-mounted directories from the host may be owned by root
+#   - Docker Desktop on Windows mounts volumes with host permissions
+#     that don't map to the container user
+chown -R "${PUID}:${PGID}" /config /data
+
+echo "[entrypoint] /config and /data ownership set to ${PUID}:${PGID}"
+
+# ── Drop privileges and exec the application ───────────────────────────────
+echo "[entrypoint] exec archivum as ${PUID}:${PGID}"
+exec su-exec "${PUID}:${PGID}" /usr/local/bin/archivum "$@"