milestone 4: org header, logging, backup docs, mark all m4 tasks done

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -157,6 +157,27 @@ synq/
 5. add history screen and resend handling.
 6. polish launch speed and widget/share-target only after core path works.
 
+## backup
+
+### what to back up
+
+the server writes to one directory (the `/data` volume). back up the whole thing:
+
+```text
+/data/synq.org        ← the canonical org capture file
+/data/capture.sqlite3 ← idempotency store (dedup ids)
+/data/token.txt       ← auto-generated token (if not using PHONE_CAPTURE_TOKEN env var)
+```
+
+on unraid the host path is whatever you mapped in compose, e.g. `/mnt/user/ben/synq/phone-capture`.
+
+### restore behavior
+
+- restore the `/data` volume to a new container and start it. the server will pick up where it left off.
+- `synq.org` is append-only plain text — it is human-readable and recoverable even without the sqlite db.
+- if `capture.sqlite3` is lost but `synq.org` is intact, the server will accept re-posted captures that were already in the org file (no dedup). the android app marks them synced either way (`already_seen` or `accepted`), so the only side effect is duplicate org entries for anything re-synced. restore the db from backup to avoid this.
+- if `token.txt` is lost, delete it and let the server generate a new one on next start, then update the app settings.
+
 ## v2 parking lot
 
 - android share target