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/service/pool_service.go

@@ -10,7 +10,7 @@ import (
 	"tanabata/backend/internal/port"
 )
 
-const poolObjectType         = "pool"
+const poolObjectType = "pool"
 const poolObjectTypeID int16 = 4 // fourth row in 007_seed_data.sql object_types
 
 // PoolParams holds the fields for creating or patching a pool.
@@ -238,4 +238,4 @@ func (s *PoolService) Reorder(ctx context.Context, poolID uuid.UUID, fileIDs []u
 		return err
 	}
 	return s.pools.Reorder(ctx, poolID, fileIDs)
-}
+}