Submissions: labeled actions + real appeal-driven unblock

Make each admin action self-explanatory and give content appeals a real
effect instead of a dead-end "Dismiss".

- submissionsSection.js: per-type action sets, each button paired with a
  one-line description. Applications show Approve (adds to whitelist) / Deny;
  appeals that name a real event show "Approve & unblock" (removes the video
  from the event block list) / "Keep blocked"; other types show "Mark handled".
- submissionService.js: parse an appeal's `e` tag into targetEventId (trusted
  only when it's a well-formed 64-char hex id).
- iframe-content-appeals-form.html: add a required "Blocked video link or
  event ID" field; regex-validate + normalize a share link / nevent / note /
  hex to the hex event id, tag it as `e`, and include it in the body. Block
  submission when no valid reference is provided.
- CSS: stacked action + hint styling; iframe-form .form-hint.
- tests: cover targetEventId parsing (valid, malformed, absent).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

css/tailwind.source.css

@@ -3231,7 +3231,24 @@
 
   .submission-card__actions {
     display: flex;
-    gap: var(--space-2xs);
+    flex-wrap: wrap;
+    gap: var(--space-sm);
+    align-items: flex-start;
+  }
+
+  /* Each action pairs its button with a one-line description so a moderator
+     knows exactly what the control does before clicking. */
+  .submission-card__action {
+    display: flex;
+    flex-direction: column;
+    gap: var(--space-3xs);
+    min-inline-size: 0;
+  }
+
+  .submission-card__action-hint {
+    font-size: var(--font-size-2xs);
+    color: var(--color-text-muted);
+    max-inline-size: 22ch;
   }
 
   /* #43: always-visible active-identity pill. Rendered after the header in
@@ -4531,6 +4548,12 @@
     margin-top: var(--space-xs);
   }
 
+  body.iframe-form .form-hint {
+    margin-top: var(--space-xs);
+    font-size: var(--font-size-2xs);
+    color: var(--color-text-muted);
+  }
+
   body.iframe-form .checkbox-group,
   body.iframe-form .radio-group {
     display: flex;