Add Lidarr tracked-data cache + duplicate artist cleanup

Shared cache (lidarr_get_tracked_data() in common.sh) so scripts stop
hitting Lidarr's live API for tracked counts every run, and stop
treating a mid-rescan dip as a genuine problem — a whole-library
RescanFolders legitimately makes trackFileCount read far below normal
while it re-verifies every file (confirmed 2026-07-16: 22% of normal
mid-scan). Cache reads fresh-if-recent, waits out an active rescan
(calibrated to that command's own historical duration, tracked per
command name since RescanFolders and DownloadedAlbumsScan take wildly
different amounts of time), then falls back to a stale cache rather
than hard-failing after a few strikes.

lidarr_cleanup.sh: no longer stacks a fresh DownloadedAlbumsScan on
top of one already running, and the tracked-count floor check now
waits out a genuine rescan instead of aborting on every overlap.

lidarr_duplicate_artist_cleanup.sh (new): finds case-insensitive
duplicate artist entries — same display name, different MusicBrainz
ID, added when a search/list-sync matches the wrong same-named artist.
Deletes the empty phantom side and blocks it from Import List
Exclusions, leaves genuinely-different-real-artists alone (checked by
album title overlap, deduped per-artist first so a legitimate reissue
under an artist's own catalog doesn't false-flag as cross-artist
overlap), and only notifies for the rare case where both sides have
real, overlapping content.

lidarr_cache_prefill.sh (new): warms the cache at array start so nothing
reads it cold after boot.

lidarr_missing_art.sh, lidarr_release_fixer.sh: write-through the cache
as a side effect of fetches they already needed for their own purposes.

Deployment/master.conf.template

@@ -300,6 +300,7 @@
         "unRAID_Essentials/php_fpm_max_children.sh"   # WebGUI performance tuning
         "unRAID_Essentials/inotify_tuning.sh"         # bump inotify limits — containers miss events if exhausted
         "Docker_Essentials/docker_network_connect.sh" # ensure networks exist + connect containers
+        "Arrs_Stack/lidarr_cache_prefill.sh"           # warm Lidarr tracked-data cache before anything reads it cold
         "Arrs_Stack/start_webhook_listener.sh"             # arr upgrade webhook listener — continuous
         "Fallback/fallback.sh"                        # mutual failover — continuous
     )
@@ -387,6 +388,7 @@
         "Media/media_cleaner.sh anime"                # remove junk from anime shares
         "Media/media_cleaner.sh media"                # remove junk from media shares
         "Arrs_Stack/lidarr_release_fixer.sh"               # fix wrong release editions before cleanup runs
+        "Arrs_Stack/lidarr_duplicate_artist_cleanup.sh"    # resolve duplicate MusicBrainz artist entries before cleanup runs
         "Arrs_Stack/lidarr_cleanup.sh"                     # remove orphaned music files
         "Arrs_Stack/sonarr_cleanup.sh"                     # remove orphaned TV files
         "Arrs_Stack/radarr_cleanup.sh"                     # remove orphaned movie files
@@ -1089,6 +1091,14 @@
                                     # protects against API returning partial data on a bad day
     LIDARR_TRACKED_COUNT_FILE="$DATA_DIR/lidarr_tracked.count"
     LIDARR_IMPORT_SCAN_TIMEOUT=600  # seconds to wait for pre-flight import scan
+
+# Lidarr tracked-data cache — shared by lidarr_cleanup.sh, lidarr_duplicate_artist_cleanup.sh,
+# lidarr_missing_art.sh, lidarr_release_fixer.sh, and lidarr_cache_prefill.sh. See
+# lidarr_get_tracked_data() in common.sh for the fresh/stale/rescan-active branching logic.
+    LIDARR_CACHE_FILE="$DATA_DIR/lidarr_tracked_cache.json"
+    LIDARR_RESCAN_DURATION_DB="$DATA_DIR/lidarr_rescan_duration.db"
+    LIDARR_CACHE_MAX_AGE_DAYS=1     # force a live refresh (or rescan-aware wait) past this age
+    LIDARR_PREFILL_WAIT_MINUTES=10  # array-start prefill: how long to retry reaching Lidarr
     LIDARR_EXTENSIONS=("flac" "mp3" "m4a" "wav" "aac" "ogg" "opus" "wma")
     LIDARR_PROTECTED_PATTERNS=(
         # Metadata