Initial implementation: extend TrueCloud Backup to S3 and B2 providers

Patches middlewared at runtime via sitecustomize.py (no file edits to /usr/)
and widens the UI credential dropdown from Storj-only to S3+B2+Storj.
Persists across TrueNAS updates via PREINIT initshutdownscript stored in DB.

patch/apply.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+# /data/truecloud-patch/apply.sh
+#
+# PREINIT script registered via TrueNAS initshutdownscript.
+# Runs on every boot before middlewared starts, re-applying patches that
+# TrueNAS updates wipe from /usr/.
+#
+# Two things are patched:
+#   1. sitecustomize.py  → monkey-patches B2 restic support + URL fix into
+#                          middlewared at Python startup time (backend)
+#   2. Angular JS bundle → adds S3 and B2 to the credential dropdown in
+#                          the TrueCloud Backup task form (UI)
+
+set -euo pipefail
+
+PATCH_DIR="/data/truecloud-patch"
+LOG="$PATCH_DIR/apply.log"
+
+{
+    echo "=== $(date -Iseconds) ==="
+
+    # ── 1. Backend: install sitecustomize.py ─────────────────────────────
+    SITE_PKG=$(python3 -c "import site; print(site.getsitepackages()[0])" 2>/dev/null || true)
+
+    if [ -z "$SITE_PKG" ]; then
+        echo "WARNING: could not determine site-packages path, skipping backend patch"
+    else
+        # If an unrelated sitecustomize.py exists, back it up once.
+        if [ -f "$SITE_PKG/sitecustomize.py" ] && \
+           ! grep -q "truecloud-patch" "$SITE_PKG/sitecustomize.py" 2>/dev/null; then
+            cp "$SITE_PKG/sitecustomize.py" "$SITE_PKG/sitecustomize.py.pre-truecloud-patch"
+            echo "Backed up existing sitecustomize.py"
+        fi
+
+        cp "$PATCH_DIR/sitecustomize.py" "$SITE_PKG/sitecustomize.py"
+        echo "Installed sitecustomize.py → $SITE_PKG/sitecustomize.py"
+    fi
+
+    # ── 2. UI: patch Angular bundle ──────────────────────────────────────
+    python3 "$PATCH_DIR/patch_ui.py"
+
+    echo "=== done ==="
+
+} >> "$LOG" 2>&1