Require camera name explicitly across all seasons scripts

No script defaults to SUNRISE_CAM (east) for the seasons pipeline.
Every direction is treated equally — camera name is a required arg,
not an optional override.

- 4-seasons.sh: $1 required, exits with usage if missing
- montage-mvt.sh: arg order changed to <cam> [date]; $1 required
- year-end-join.sh: $2 (cam) required
- verify-mvt.sh: $4 (cam) required
- migrate-seasons.sh: example commands updated to new arg order
- README.md: montage-mvt.sh examples updated

https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ

4-seasons.sh

@@ -13,8 +13,13 @@ SCRIPT_DIR="$(dirname "$(realpath "$0")")"
 source "$SCRIPT_DIR/sky-cam.conf"
 export TIMEZONE   # make it visible to season_info.py subprocess
 
-# Camera name: first argument overrides conf (systemd passes it via ExecStart).
-CAM_NAME="${1:-$SUNRISE_CAM}"
+# Camera name: required first argument (systemd passes it via ExecStart).
+CAM_NAME="${1:-}"
+if [ -z "$CAM_NAME" ]; then
+    echo "Usage: $0 <camera-name>"
+    echo "  e.g. $0 east   or   $0 north"
+    exit 1
+fi
 
 # ── Configuration ──────────────────────────────────────────────────────────────
 base_dir="$BASE_DIR"
@@ -125,5 +130,5 @@ if [ "$IS_LAST_DAY" = "true" ]; then
     echo "Last day of $SEASON Mvt $MVT_NUM — triggering montage compilation..."
     # Pass $yesterday so montage-mvt.sh looks up the correct movement
     # (running the next morning, "today" would already be the next movement).
-    "$SCRIPT_DIR/montage-mvt.sh" "$yesterday" "$CAM_NAME"
+    "$SCRIPT_DIR/montage-mvt.sh" "$CAM_NAME" "$yesterday"
 fi