feat(partnership): extract transfer into partnership_transfer.sh

Follows the same extraction pattern as partnership_offboard.sh.
partnership_manager.sh --transfer now exec-forwards to the new script.
Legacy inline block preserved under `if false` for reference.

Fixes in partnership_transfer.sh vs the original inline code:
- WebUI reconfiguration corrected: SSH to new owner (mirror) to set localhost;
  reconfigure_local_webuis() on current server to point to new owner IP
- master.conf remote update uses scp push instead of self-SSH with wrong path
- SSH key uses $SSH_KEY directly (was using undefined {HOST*}_SSH_KEY expansion)

Partnership/partnership_manager.sh

@@ -1545,6 +1545,13 @@ fi
 # ━━━ Transfer ━━━
 # ==============================================================================================
 if [[ "$MODE" == "transfer" ]]; then
+    exec bash "$SCRIPT_DIR/partnership_transfer.sh" \
+        ${TRANSFER_CONFIRM_INPUT:+--confirm="$TRANSFER_CONFIRM_INPUT"} \
+        "${FILTERED_ARGS[@]}"
+fi
+
+# (legacy inline transfer block — kept below for reference, unreachable)
+if false; then
     echo ""
     echo "━━━ $ICON_FALLBACK Transfer Ownership — $(date '+%Y-%m-%d %H:%M:%S') ━━━"
     echo ""