chore: bind-mount postgres/redis data dirs, update docs for pocketveto.org

- docker-compose.yml: replace named volumes with ./postgres/data and ./redis/data bind mounts
- .gitignore: exclude postgres/ and redis/ data directories
- DEPLOYING.md: update clone URL to public PocketVeto repo
- UPDATING.md: fix paths (~/pocketveto), clone URL, webhook IDs

Authored by: Jack Levy

.gitignore

@@ -15,5 +15,7 @@ frontend/.next/
 frontend/node_modules/
 frontend/out/
 
-# Docker
+# Docker — bind-mount data directories (created on first run)
+postgres/
+redis/
 *.log