fix: keep the mirror out of the device root

Proton refuses a file directly in a device's root folder — 422 "Cannot
create file at the root of a device" — so the first real backup died on
RESTORE.txt, before it had written anything. The mirror now lives in a
`data/` folder on the device, which is both what Proton permits and the
honest name for what it holds: the contents of DIARY_DATA_DIR.

Every remote path changed with it, so the bookkeeping describing the old
layout is dropped and rebuilt on the next run. A device root that
already collected an empty `uploads/` folder from the failed attempt
keeps it; it is not ours to guess about, and deleting it is one click.

Also quiet rPGP's packet-header warnings by default. They fire on every
key Proton wrote slightly differently to how rPGP re-serialises it —
cosmetic, once per unlock, and loud enough to bury the backup's own log.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D5Gk8FPkRXu1e6Nj2BCRE1

README.md

@@ -114,16 +114,17 @@ it has been quiet for `DIARY_BACKUP_DEBOUNCE_SEC` the mirror runs, with
 sixty. The device folder ends up as a copy of the data directory:
 
 ```text
-narl-diary/
-  RESTORE.txt        what this is, and how to put it back
-  diary.db           a VACUUM INTO snapshot — consistent, no write-ahead log
-  uploads/<uuid>     every uploaded file, under the name the database knows
+narl-diary/          the device — Proton allows only folders in a device root
+  data/              the diary's data directory, copied
+    RESTORE.txt      what this is, and how to put it back
+    diary.db         a VACUUM INTO snapshot — consistent, no write-ahead log
+    uploads/<uuid>   every uploaded file, under the name the database knows
 ```
 
 `diary.db` becomes a new revision each time, so Proton Drive keeps the older
 ones and a mistake that was mirrored can still be undone. Uploads are written
-once and never rewritten. Restoring is copying both back into an empty data
-directory — no tool in between, which is the point.
+once and never rewritten. Restoring is copying the contents of `data/`
+back into an empty data directory — no tool in between, which is the point.
 
 | command | what it does |
 | --- | --- |