style(project): format Go with gofmt, set up Prettier for the frontend

Run gofmt -w across the backend, normalising the manually-aligned := blocks
to the gofmt standard. No code behaviour changes.

Add Prettier (+ prettier-plugin-svelte) to the frontend with the SvelteKit
default config (tabs, single quotes) so formatting is reproducible, then run
it over the whole tree. Add format / format:check npm scripts and a
.prettierignore (build output, generated schema.ts, static assets).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/internal/db/postgres/pool_repo.go

@@ -712,4 +712,4 @@ func (r *PoolRepo) Reorder(ctx context.Context, poolID uuid.UUID, fileIDs []uuid
 	}
 
 	return r.reassignPositions(ctx, q, poolID, ordered)
-}
+}