chore(credits): drop the "About this work" section — it moves to the About page

The CC BY-SA work-license declaration ("About this work") was on the credits
page, but the About page (built on the parallel feat/accessibility-pass) will
own that content; keeping it in both places would duplicate it. Remove the
section from credits.html and make the footage note self-contained (it still
states the footage is altered — the per-clip "indicate modifications" cue stays
with the attributions). Tests updated to assert the declaration is intentionally
no longer on the credits page. The .declaration CSS rule is left in place for the
About page to reuse.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

simulator/unit/credits.test.js

@@ -55,8 +55,10 @@ test("credits.html wires config.js + credits.js, the attributions container, and
   assert.match(html, /href="index\.html"/);           // back into the experience
 });
 
-test("credits.html carries the CC BY-SA derivative declaration (Option D1)", () => {
+test("credits.html notes footage is altered; the work-license declaration lives on the About page", () => {
   const html = fs.readFileSync(path.join(__dirname, "../static/credits.html"), "utf8");
-  assert.match(html, /CC BY-SA 4\.0/);                 // the altered work's own license
-  assert.match(html, /altered/i);                      // states the footage is modified
+  assert.match(html, /altered/i);                      // modification indicated alongside the attributions
+  // The CC BY-SA work-license declaration ("About this work") moved off the credits
+  // page onto the About page — it must NOT be duplicated here.
+  assert.doesNotMatch(html, /CC BY-SA 4\.0/);
 });