shim: shorten subtitle stream labels in detail dropdowns

Stock Jellyfin renders subtitle stream entries as
"<lang> - <CODEC> - (External|Internal|Embedded)[ - flag]". For ARRFLIX,
which has at most one subtitle format per language, the codec and source
suffix are noise. Add a small JS shim to web-overrides/index.html that
matches that exact shape and collapses the label to "<lang>" (with
"(Forced)" / "(SDH)" / "(Hearing Impaired)" if those flags are
present; "Default" is dropped since it's redundant when there's only one
stream of that language).

Audio labels like "5.1Ch Surround Sound - English - AAC - Stereo - Default"
have a different number of segments and don't match, so they pass through
untouched.

The shim runs after DOMContentLoaded and re-walks any nodes added later
via MutationObserver (covers actionsheet dropdowns that mount lazily).

Bracketed by /* SUB-LABEL-SHIM-BEGIN */ and /* SUB-LABEL-SHIM-END */
markers; bin/revert-sub-label-shim.sh deletes between the markers in one
sed pass and saves a timestamped backup. No container restart needed
(index.html is bind-mounted).

bin/revert-sub-label-shim.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+# Revert the SUB-LABEL-SHIM injected into web-overrides/index.html on 2026-05-10.
+#
+# What it removes:
+#   /* SUB-LABEL-SHIM-BEGIN ... */ ... /* SUB-LABEL-SHIM-END */
+#
+# Idempotent: safe to re-run.
+# After reverting, hard-refresh the browser (Ctrl+Shift+R) so the cached
+# index.html is fetched fresh.
+
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+TARGET="$REPO_ROOT/web-overrides/index.html"
+
+if [[ ! -f "$TARGET" ]]; then
+  echo "ERROR: $TARGET not found" >&2
+  exit 1
+fi
+
+if ! grep -q "SUB-LABEL-SHIM-BEGIN" "$TARGET"; then
+  echo "shim already absent — nothing to do"
+  exit 0
+fi
+
+cp "$TARGET" "$TARGET.bak.$(date -u +%Y%m%dT%H%M%SZ)"
+
+# delete from BEGIN marker line through END marker line, inclusive
+sed -i '/SUB-LABEL-SHIM-BEGIN/,/SUB-LABEL-SHIM-END/d' "$TARGET"
+
+if grep -q "SUB-LABEL-SHIM" "$TARGET"; then
+  echo "ERROR: revert left orphan markers in $TARGET" >&2
+  exit 2
+fi
+
+echo "reverted. backup at $TARGET.bak.*"
+echo "next: container needs no restart (index.html is bind-mounted); hard-refresh browser."