Unify Iron Coast mission names and cinematic mission previews

mods/iron_coast_mission_3/README.md

@@ -1,8 +1,8 @@
-# Iron Coast — Mission 3: Saltworks Convoy
+# Iron Coast S1 M03: Saltworks Convoy
 
 API 1 package, version 1.0.1. Enable it in Mods at the main menu and apply the selection. The normal dependency selection also enables `iron_coast_scout`, `iron_coast_turret`, `iron_coast_boss_3`, `pulse_cannon`, `seeker_swarm`, `ion_lance`, `iron_coast_music`.
 
-Mission `iron_coast_mission_3:mission_03`: **Iron Coast 3 — Saltworks Convoy**. Destroy three cargo transports, two escort turrets and Saltbreaker. Required ground objectives remain reachable; escaping optional aircraft never counts as a kill. Elapsed time alone does not finish the mission.
+Mission `iron_coast_mission_3:mission_03`: **Iron Coast S1 M03: Saltworks Convoy**. Destroy three cargo transports, two escort turrets and Saltbreaker. Required ground objectives remain reachable; escaping optional aircraft never counts as a kill. Elapsed time alone does not finish the mission.
 
 Scheduled spawn totals for Training / Rookie / Veteran / Elite are **32 / 45 / 58 / 71**. These are enabled scheduled entries, not simultaneous live-enemy counts. Groups can overlap when earlier enemies survive.
 
@@ -11,3 +11,15 @@ Align the forward guns with required targets while moving around incoming shots.
 ## Validation and history
 
 See the [current Iron Coast retune results and limits](../../docs/iron-coast-retune.md). Package-local acceptance reports, validation results and retained test sources describe pre-retune 1.0 behavior unless a result explicitly identifies the newer package and runner. They remain historical material, not current playthrough guarantees.
+
+## Rebuilding the briefing
+
+Run `python3 art/build_cinematic_briefing.py` from this package directory
+(Pillow required). It verifies the unchanged cinematic master and rebuilds the
+exact SD/HD filenames referenced by `content.json`; the prompt and provenance
+are beside the master in `art/`. This artwork update changes package hashes;
+existing pilots use the normal changed-mod confirmation, with stable IDs and
+saved equipment/progression retained.
+
+`build_assets.py` also includes the cinematic briefing recipe when rebuilding
+this package's assets; its tile, sprite and sound processing is unchanged.