fix(infra): simplify PostgreSQL backup to pg_dumpall + pg_basebackup

pgBackRest as Docker sidecar was overly complex (needs shared WAL
directory, stanza management, special entrypoint). Replace with a
simpler, proven approach using native PostgreSQL tools:

Backup container (postgres:16-alpine):
- Hourly: pg_dumpall | gzip (all databases as SQL, ~2 day retention)
- Daily 03:00: pg_basebackup -Ft -z (physical backup, 30 day retention)
- Auto-cleanup of old backups
- Storage: /Volumes/ManaData/backups/postgres/

Also: Remove pgbackrest.conf, simplify postgresql.conf (remove WAL
archiving config, keep performance tuning + replication for basebackup)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/postgres/postgresql.conf

@@ -1,23 +1,19 @@
-# PostgreSQL Configuration for WAL Archiving + pgBackRest
-# Append to default postgresql.conf
+# PostgreSQL Performance Tuning for Mac Mini (16GB RAM)
+# Shared with ~70 other containers, so conservative settings
 
-# WAL Archiving (required for Point-in-Time Recovery)
-wal_level = replica
-archive_mode = on
-archive_command = 'pgbackrest --stanza=mana archive-push %p'
-archive_timeout = 60
-
-# WAL Settings (tuned for 16GB Mac Mini)
-max_wal_senders = 3
-max_wal_size = 1GB
-min_wal_size = 80MB
-
-# Performance (tuned for 16GB RAM, shared with other services)
+# Performance
 shared_buffers = 512MB
 effective_cache_size = 2GB
 work_mem = 16MB
 maintenance_work_mem = 128MB
 
+# WAL Settings
+max_wal_size = 1GB
+min_wal_size = 80MB
+
+# Replication (for pg_basebackup)
+max_wal_senders = 3
+
 # Logging
 log_min_duration_statement = 1000
 log_checkpoints = on