Add full banner headers to all scripts across the codebase

Every script now has the established header format: PURPOSE with ─────── separator,
OPERATIONAL MODEL, DESIGN PRINCIPLES, OPERATIONAL SAFEGUARDS, CONFIGURATION, and
RUNTIME MODES — structured with full ====== banner sections throughout.

Orchestrators converted from compact ── inline format to full banners. Stale
emby-fallback and dirty sync references removed from Plugin/user_script_plug-in.sh.

Media/play_state_sync.sh

@@ -33,6 +33,38 @@
 #   The higher tick count wins.
 #
 # ==============================================================================================
+# DESIGN PRINCIPLES
+# ==============================================================================================
+#
+# Newest Timestamp Wins
+#   No merge logic, no conflict resolution — the server with the most recent
+#   LastPlayedDate is simply authoritative. Simple rules produce predictable
+#   outcomes users can reason about.
+#
+# No Data Loss
+#   The sync only pushes state forward — it never clears a Played flag or
+#   resets a resume position to zero. A watch record on any server always
+#   propagates outward, never disappears.
+#
+# Provider ID Matching
+#   Items are matched by external IDs (IMDb, TVDB, MusicBrainz), not by
+#   title or file path. This makes matching robust across library reorganisation,
+#   renames, and multi-server path differences.
+#
+# ==============================================================================================
+# OPERATIONAL SAFEGUARDS
+# ==============================================================================================
+#
+#   PLAY_SYNC_ENABLED gate   — exits cleanly when disabled; no partial runs
+#   PARTNERSHIP gate         — skips remote sync when partnership is inactive
+#   Per-server reachability  — unreachable servers are skipped individually;
+#                              one offline server does not abort the entire sync
+#   User match required      — a user missing from a server is skipped for that
+#                              server; no cross-account state pollution
+#   acquire_lock             — prevents concurrent runs from racing on the same
+#                              items during the 30-minute critical window
+#
+# ==============================================================================================
 # CONFIGURATION (host*.conf, aliased by detect_hosts)
 # ==============================================================================================
 #