fix(cctv): make the NYC DOT pack opt-in and carry DOT's disclaimer

NYC DOT asks developers who use its camera feed to sign a data-sharing
agreement, and this project does not hold one that covers downstream
installs. The pack now loads only when CCTV_NYC_ENABLED=1; unset, empty
or any other value makes no request to webcams.nyctmc.org (tested).

The NYC credit carries NYC DOT's requested application disclaimer
verbatim, and DATA_SOURCES, README, CHANGELOG, CURRENT-STATE and
.env.example describe the prerequisite.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/data/dataCredits.js

@@ -91,6 +91,13 @@ export function hideOsmCredit(viewer, owner) {
   return true;
 }
 
+/** NYC DOT asks every application that uses its data to carry this
+ * disclaimer verbatim (nyc.gov/html/dot/html/about/datafeeds.shtml). */
+export const NYC_DOT_DISCLAIMER =
+  'This application may contain and/or utilize information which was originally compiled by the New York City Department of Transportation (NYC DOT) for governmental purposes; the information may subsequently been modified by entity/entities other than NYC DOT. ' +
+  'NYC DOT and the City of New York make no representation as to the accuracy or usefulness of the information provided by this application or the information's suitability for any purpose and disclaim any liability for omissions or errors that may be contained therein. ' +
+  'The public is advised to observe posted signage for compliance with applicable laws and regulations.';
+
 export const DATA_CREDITS = [
   // ── Live sources ────────────────────────────────────────────────
   {
@@ -250,8 +257,9 @@ export const DATA_CREDITS = [
   {
     key: 'nyc-cctv',
     html:
-      'CCTV cameras & frames (New York City): ' +
-      '<a href="https://webcams.nyctmc.org/" target="_blank" rel="noopener">NYC DOT Traffic Management Center</a>',
+      'CCTV cameras &amp; frames (New York City, when enabled): ' +
+      '<a href="https://webcams.nyctmc.org/" target="_blank" rel="noopener">NYC DOT Traffic Management Center</a>. ' +
+      NYC_DOT_DISCLAIMER,
   },
   {
     key: 'gbfs',