feat: replace SFTP drop with Syncthing share path

Remove SFTPGo; mount event data from the Syncthing folder, watch
incoming/, and name variants after the source stem.

Co-authored-by: Cursor <cursoragent@cursor.com>

SOUL.md

@@ -6,23 +6,24 @@
 
 ## One-Liner
 
-Event photo pep pipeline: SFTP -> gmic/rembg -> web. Upload a photo at the
-event, get back weird/fun filtered variants seconds later.
+Event photo pep pipeline: Syncthing drop -> gmic/rembg -> web. Upload a
+photo at the event, get back weird/fun filtered variants seconds later.
 
 ## Vision
 
-At an event (f12 meetup/party), someone drops a photo into an SFTP inbox
-from a laptop/camera rig. A worker rips the background off, runs it
+At an event (f12 meetup/party), someone drops a photo into a Syncthing
+folder from a phone/camera rig. A worker rips the background off, runs it
 through a random gmic filter/blend chain, and a handful of variants show
 up on a shared web page almost immediately — no app install, no login, no
 waiting for someone to "process the photos later". If a variant is fun,
-remix it with different filters right there.
+remix it with different filters right there. Finished jobs sync back to
+the phone via the same Syncthing share.
 
 ## Audience
 
 Event organizers and attendees at f12 events, on their phones, often on
 bad venue wifi. Nobody signs up, nobody logs in. Whoever has the link
-(and whoever's uploading from the SFTP side) is the whole audience.
+(and whoever's syncing photos in) is the whole audience.
 
 ## Tone & Wording
 
@@ -41,7 +42,7 @@ bad venue wifi. Nobody signs up, nobody logs in. Whoever has the link
 |---------|------|-----|
 | Success | `Remix erzeugt.` | `Dein Kunstwerk ist fertig! 🎉` |
 | Error | `Foreground-Filter fehlgeschlagen: Timeout nach 120s` | `Etwas ist schiefgelaufen.` |
-| Empty state | `Noch keine Jobs. Bild per SFTP hochladen, dann kurz warten.` | `Hier ist noch nichts los... lade doch was hoch! 😊` |
+| Empty state | `Noch keine Jobs. Bild in den Sync-Ordner legen, dann kurz warten.` | `Hier ist noch nichts los... lade doch was hoch! 😊` |
 
 ## Design
 
@@ -55,33 +56,32 @@ bad venue wifi. Nobody signs up, nobody logs in. Whoever has the link
 
 - No web auth / accounts / login product — anyone with the link sees
   everything, by design, for this event tool.
-- No camera-to-phone client — upload path is SFTP only.
+- No camera-to-phone client in this repo — upload path is Syncthing
+  (phone/folder setup is out of band).
 - No beamer/projector product built into this repo.
 - Not a DAM (digital asset manager) — no albums, tagging, search,
-  retention policies. `inbox/` and `jobs/` are the whole data model.
-- No auto-deletion of inbox uploads. Ever. The worker only reads/copies.
+  retention policies. `incoming/` and `jobs/` are the whole data model.
+- No auto-deletion of incoming uploads. Ever. The worker only reads/copies.
+- No Syncthing container in this compose — Syncthing runs on the host.
 
 ## Infrastructure (project-local)
 
 - Workdir on server: `/home/frank/live.f12.rocks`
-- Data volume: `${DATA_HOST_DIR}` (default `./data` locally, absolute
-  path `/home/frank/live.f12.rocks/data` on the server) — bind-mounted
-  into all three services (`sftpgo`, `worker`, `web`) at different
-  container paths, see `compose.yml` header comment.
-- SFTP: host port `12121` -> `sftpgo:2022` (spec `121212` is not a valid
-  TCP port). SFTPGo web admin is never
-  exposed (internal-only, port 8080, no Traefik route).
+- Data volume (Syncthing share): `${DATA_HOST_DIR}` — prod default
+  `/home/frank/sync.schwenk.online/data/livef12`, local override `./data`.
+  Bind-mounted into `worker` and `web` at `/data` (see `compose.yml`).
+- Layout under the share: `incoming/` (phone drop), `jobs/` (full tree
+  syncs back), `processed.json`.
 - Domain: `live.f12.rocks`, routed via the shared external `traefik`
   network, TLS via `myresolver` (see `INFRASTRUCTURE.md`).
-- rembg model cache and SFTPGo host keys live in named Docker volumes
-  (`rembg_cache`, `sftpgo_state`), not under `./data` — they're
-  container state, not event data.
+- rembg model cache lives in the named Docker volume `rembg_cache`, not
+  under the Syncthing share — container state, not event data.
 
 ## Project-Specific Rules
 
 ```markdown
-- Never delete or move files under inbox/ from worker code — SFTP is the
-  only writer there. (reason: uploads are the one copy of the original
+- Never delete or move files under incoming/ from worker code — Syncthing
+  is the writer there. (reason: uploads are the one copy of the original
   that exists outside a phone's camera roll)
 - Keep every intermediate image in jobs/<id>/intermediates/ — don't clean
   them up automatically. (reason: useful for debugging bad filter picks,