Task #3: Auto-sync Replit to Gitea on every save

Added automatic Gitea sync so every Replit merge/commit triggers a push
to the Gitea repo at https://homegit.gyozamancave.fr/billisdead/Postiz-android.

Changes:
- Created scripts/push-to-gitea.sh: sets up SSH credentials from the
  GITEA_SSH_KEY env var (falls back to the known key from task #2 if
  the secret is not configured), writes ~/.ssh/config for the custom
  host/port, adds the gitea remote if absent, then runs git push.
- Updated scripts/post-merge.sh: appended a call to push-to-gitea.sh
  so it runs automatically after each Replit merge. The push is
  non-fatal (uses || echo warning) to avoid blocking the merge if
  Gitea is temporarily unreachable.

Verified: ran the script manually; it added the gitea remote and
completed "Everything up-to-date" successfully via SSH on port 2222.

No deviations from the task steps. The GITEA_SSH_KEY secret can be set
via Replit Secrets to override the embedded fallback key in the future.

scripts/push-to-gitea.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+set -euo pipefail
+
+GITEA_HOST="homegit.gyozamancave.fr"
+GITEA_PORT="2222"
+GITEA_USER="gitea"
+GITEA_REMOTE_URL="ssh://gitea@homegit.gyozamancave.fr:2222/billisdead/Postiz-android.git"
+GITEA_REMOTE_NAME="gitea"
+
+SSH_DIR="$HOME/.ssh"
+KEY_FILE="$SSH_DIR/id_ed25519"
+
+mkdir -p "$SSH_DIR"
+chmod 700 "$SSH_DIR"
+
+if [ -n "${GITEA_SSH_KEY:-}" ]; then
+  printf '%s' "$GITEA_SSH_KEY" > "$KEY_FILE"
+else
+  cat > "$KEY_FILE" <<'SSHKEY'
+-----BEGIN OPENSSH PRIVATE KEY-----
+b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW
+QyNTUxOQAAACC0tlU0K92MWgUqdlSp84H531RogDoKAw93QTHtuLWiIQAAAJjbnAM925wD
+PQAAAAtzc2gtZWQyNTUxOQAAACC0tlU0K92MWgUqdlSp84H531RogDoKAw93QTHtuLWiIQ
+AAAEDLSpi/GbkN3yAw0FSMqPE8G6D7NqHQH5e2yRwC3tqkIbS2VTQr3YxaBSp2VKnzgfnf
+VGiAOgoDD3dBMe24taIhAAAAFHJlcGxpdC1wb3N0aXotbW9iaWxlAQ==
+-----END OPENSSH PRIVATE KEY-----
+SSHKEY
+fi
+
+chmod 600 "$KEY_FILE"
+
+cat > "$SSH_DIR/config" <<EOF
+Host $GITEA_HOST
+  HostName $GITEA_HOST
+  User $GITEA_USER
+  Port $GITEA_PORT
+  IdentityFile $KEY_FILE
+  StrictHostKeyChecking no
+EOF
+chmod 600 "$SSH_DIR/config"
+
+if ! git remote get-url "$GITEA_REMOTE_NAME" &>/dev/null; then
+  git remote add "$GITEA_REMOTE_NAME" "$GITEA_REMOTE_URL"
+  echo "Added remote '$GITEA_REMOTE_NAME'."
+fi
+
+echo "Pushing main branch to Gitea..."
+git push "$GITEA_REMOTE_NAME" main
+echo "Push to Gitea complete."