Stage 0: migrate pipeline scripts from /opt/sldl, scaffold repo

Moves all ~30 pipeline scripts, configs, and the vendored sldl binary into
this repo (source /opt/sldl left untouched). Removes all docker exec/docker
compose dependencies now that beets and sldl run in-process/as a subprocess
of this container instead of via soulbeet/on-demand sldl containers.
Replaces hardcoded host paths, Navidrome credentials, and Spotify credential
sourcing with env-var-driven paths and shared credential loaders. Adds
Dockerfile, entrypoint.sh, requirements.txt, docker-compose.snippet.yml, and
the initial app DB schema.

pipeline/lib/gen-djmix-playlist.sh

@@ -0,0 +1,62 @@
+#!/bin/bash
+# gen-djmix-playlist.sh — regenerate djmix.m3u8 from the configured album list.
+#
+# Reads ${ALEMBIC_CONFIG_DIR:-/config}/pipeline/djmix-albums.txt (one beets query per line),
+# collects all matching track paths, deduplicates, and writes
+# ${MUSIC_DATA_DIR:-/data/music}/playlists/djmix.m3u8.
+#
+# Azuracast imports this playlist so DJ mixes can be excluded from general
+# rotation. Navidrome also picks it up as a regular playlist.
+#
+# Runs daily from cron. Safe to run manually anytime.
+
+set -u
+
+CONFIG=${ALEMBIC_CONFIG_DIR:-/config}/pipeline/djmix-albums.txt
+PLAYLIST_DIR=${MUSIC_DATA_DIR:-/data/music}/playlists
+OUT="${PLAYLIST_DIR}/djmix.m3u8"
+LOG_DIR=${ALEMBIC_CONFIG_DIR:-/config}/logs
+LOG="${LOG_DIR}/djmix-$(date +%Y%m%d).log"
+
+mkdir -p "$LOG_DIR" "$PLAYLIST_DIR"
+
+log() { echo "[$(date -Iseconds)] $*" | tee -a "$LOG"; }
+
+log "=== Regenerating djmix.m3u8 ==="
+
+TRACKS=$(mktemp)
+
+while IFS= read -r query; do
+  [[ -z "$query" || "$query" == "#"* ]] && continue
+  # Split on | to support multi-field queries (e.g. "albumartist::Foo | album:Bar").
+  # Each |-separated part becomes a separate beet query term (ANDed together).
+  # Single-field lines (no |) are passed as one arg so commas in album names
+  # don't get misinterpreted by beet's query parser.
+  IFS='|' read -ra _terms <<< "$query"
+  _args=()
+  for _t in "${_terms[@]}"; do
+    # strip leading/trailing whitespace
+    _t="${_t#"${_t%%[![:space:]]*}"}"
+    _t="${_t%"${_t##*[![:space:]]}"}"
+    [[ -n "$_t" ]] && _args+=("$_t")
+  done
+  beet ls -f '$path' "${_args[@]}" 2>>"$LOG" >> "$TRACKS"
+done < "$CONFIG"
+
+# Deduplicate and sort
+SORTED=$(sort -u "$TRACKS")
+rm -f "$TRACKS"
+
+COUNT=$(echo -n "$SORTED" | grep -c '^' || true)
+
+if [[ "$COUNT" -gt 0 ]]; then
+  {
+    echo "#EXTM3U"
+    echo "$SORTED"
+  } > "$OUT"
+  log "djmix.m3u8 updated with $COUNT tracks"
+else
+  log "WARNING: no tracks found — djmix.m3u8 not updated"
+fi
+
+log "=== Finished ==="