feat: rename service to galo, add halo branding and release build

- rename Go module, binary, systemd unit, PG_DATABASE default, frontend package and docs from shared-album to galo
- add theme-aware halo emblem and favicon (new ui-branding capability)
- add make build-release (versioned, stripped, static binary) and run the binary from the repo root

.env.example

@@ -3,7 +3,7 @@ PG_HOST=pg.localnet
 PG_PORT=5432
 PG_USER=album
 PG_PASSWORD=change_me
-PG_DATABASE=shared_album
+PG_DATABASE=galo
 PG_SSLMODE=disable
 
 # Metadata backend: sqlite (default, embedded single instance) or postgres