fix(gate): the plan-code guard catches decision codes, and the purge takes them

A plan's decision ids (`D1`, `D4`, `D6-A`) cited in 11 comments and test titles named a document
no reader of this repo has, and the guard had no pattern for them. It has now (mirrored in
audit_metrics), with cases for each form the citations took and for the look-alikes it must leave
alone (a JPEG marker, "3D"); the 11 lines say their why without the id. Case test seen red without
the pattern, the scan red on a planted `D9:`.

frontend/src/components/ShareDialog.tsx

@@ -235,7 +235,7 @@ function LinkShare({ job }: { job: DownloadJob }) {
     queryFn: () => api.downloadLinks(job.id),
   });
   const [creating, setCreating] = useState(false);
-  // D1: downloadable by default — matches the one-click Share (which relies on the backend
+  // Downloadable by default — matches the one-click Share (which relies on the backend
   // default) and the common "let them have the file" intent. The owner can uncheck it here.
   const [allowDownload, setAllowDownload] = useState(true);
   const [expiryDays, setExpiryDays] = useState<number | null>(null);
@@ -260,7 +260,7 @@ function LinkShare({ job }: { job: DownloadJob }) {
   });
 
   // Open with a link already generated: sharing is almost always the goal, so mint a default
-  // (no password, no expiry, downloadable per D1) link the moment the dialog finds none — as if the
+  // (no password, no expiry, downloadable) link the moment the dialog finds none — as if the
   // user had pressed "New link" → "Create". All further controls (password, download toggle, expiry,
   // extra links, revoke) stay available on the created link and via the "New link" button.
   const autoTried = useRef(false);