feat(gitsync): synka wiki-repot mot remote över SSH

- ed25519-deploy-nyckel genereras av servern (config-volymen, 0600),
  GIT_SSH_COMMAND med egen known_hosts (accept-new)
- inställningar: remote-URL, live-gren, read-only, auto-synk-intervall
- bakgrundssynk: endast fast-forward, flaggar attention vid merge-behov
- pull/push, skapa/byt gren, merge-popup (ours/theirs per fil eller allt),
  abort, reset från remote med automatisk backup-gren
- headless-konfig via config.json eller updateGitSync-mutationen
- openssh-client tillagd i runtime-imagen; mutex kring alla git-operationer

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

docker/Dockerfile

@@ -38,7 +38,8 @@ FROM alpine:3.20
 
 # su-exec: lightweight tool to drop privileges (replaces gosu / setpriv).
 # git: needed for wiki commit operations.
-RUN apk add --no-cache su-exec git
+# openssh-client: git-sync over ssh:// remotes (git shells out to ssh)
+RUN apk add --no-cache su-exec git openssh-client
 
 # Create the app group and user that the entrypoint will run as.
 # PUID/PGID can be overridden at runtime via environment variables;