Read a PDF where it is imported, and keep the text with the file

A PDF was searchable on a device once that device had opened it, because
the extracted text lived in that browser's IndexedDB and nowhere else. So
a document imported on the desktop was invisible to a search on the
phone — which is exactly the case that matters for filing invoices, since
those are imported and then never opened again.

The reading still never happens on the server. It has no PDF library and
is not getting one: the bytes arrive encrypted and are stored that way.
The device that imports the file reads it there and then, and the result
is stored beside the file in attachments.text_index, encrypted at rest
like everything else and opaque to the server. Every other device asks
for it after login and can then find a document it has never downloaded.

Not storing it was the earlier decision, on the reasoning that text
derivable from bytes the server already holds should not be kept twice.
True, and useless. A few hundred kilobytes against a file measured in
megabytes is a trade worth making.

A `null` answer is not an error — it means nobody has read this file yet.
Documents extracted before this existed are sent up the next time they
are opened.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -31,10 +31,10 @@ Diese Punkte sind Entscheidungen von Marc, keine offenen Fragen:
 Beides muss vor einem Push grün sein.
 
 ```bash
-# Unit (224 Tests, ~4 s)
+# Unit (~4 s)
 docker run --rm -v "$PWD/frontend:/w" -w /w node:20-alpine npx vitest run
 
-# Browser, zwölf Suiten (~263 Checks) – braucht den Dev-Stack
+# Browser, zwölf Suiten – braucht den Dev-Stack
 ./e2e/run.sh                 # alle
 ./e2e/run.sh editor drawing  # einzelne
 ```