Make the platform list shared across users; keep games private

Platforms no longer have a user_id: there's one global list, unique by
name, that every authenticated user reads from and writes to. Games are
unchanged - still private per user, still referencing platform_id.

- Migration: dropped platform.user_id and its FK, UNIQUE(user_id, name) ->
  UNIQUE(name), index on change_seq alone instead of (user_id, change_seq).
  Amended the one init migration in place rather than stacking a second one,
  since nothing is deployed yet.
- db/query.sql: platform queries no longer take a user_id parameter.
  DeletePlatform's NOT EXISTS guard already checked games from any user (it
  never filtered the subquery by user_id), so deleting a shared platform is
  correctly blocked by any user's games on it, not just the deleter's.
- routes.go: platform handlers still require auth (the list isn't public to
  anonymous requests) but no longer scope by user.
- Tests: updated the mocks for the new signatures, added
  TestListPlatformsIsSharedAcrossUsers.

Verified against a real Postgres: user A creates "PC", user B sees it
immediately, both can add games against it, each only sees their own
games, deleting the platform is blocked while either user has a game on
it, and the name stays globally unique.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/db/query.sql.go

@@ -70,25 +70,20 @@ func (q *Queries) CreateGame(ctx context.Context, arg CreateGameParams) (CreateG
 
 const createPlatform = `-- name: CreatePlatform :one
 INSERT INTO platform (
-  user_id, name
+  name
 ) VALUES (
-  $1, $2
+  $1
 )
 RETURNING id, name
 `
 
-type CreatePlatformParams struct {
-	UserID uuid.UUID
-	Name   string
-}
-
 type CreatePlatformRow struct {
 	ID   uuid.UUID
 	Name string
 }
 
-func (q *Queries) CreatePlatform(ctx context.Context, arg CreatePlatformParams) (CreatePlatformRow, error) {
-	row := q.db.QueryRow(ctx, createPlatform, arg.UserID, arg.Name)
+func (q *Queries) CreatePlatform(ctx context.Context, name string) (CreatePlatformRow, error) {
+	row := q.db.QueryRow(ctx, createPlatform, name)
 	var i CreatePlatformRow
 	err := row.Scan(&i.ID, &i.Name)
 	return i, err
@@ -177,24 +172,20 @@ func (q *Queries) DeleteGame(ctx context.Context, arg DeleteGameParams) (int64,
 const deletePlatform = `-- name: DeletePlatform :execrows
 UPDATE platform
 SET deleted_at = now()
-WHERE platform.id = $1 AND platform.user_id = $2 AND platform.deleted_at IS NULL
+WHERE platform.id = $1 AND platform.deleted_at IS NULL
   AND NOT EXISTS (
     SELECT 1 FROM game
     WHERE game.platform_id = platform.id AND game.deleted_at IS NULL
   )
 `
 
-type DeletePlatformParams struct {
-	ID     uuid.UUID
-	UserID uuid.UUID
-}
-
 // Soft delete, so the FK on game.platform_id is never touched and never
 // blocks this on its own; the NOT EXISTS guard is what stops a platform
-// that still has active games from being deleted. Call GetPlatform first to
-// tell "not found" apart from "blocked by games" when this affects 0 rows.
-func (q *Queries) DeletePlatform(ctx context.Context, arg DeletePlatformParams) (int64, error) {
-	result, err := q.db.Exec(ctx, deletePlatform, arg.ID, arg.UserID)
+// that still has active games - from any user, since the list is shared -
+// from being deleted. Call GetPlatform first to tell "not found" apart from
+// "blocked by games" when this affects 0 rows.
+func (q *Queries) DeletePlatform(ctx context.Context, id uuid.UUID) (int64, error) {
+	result, err := q.db.Exec(ctx, deletePlatform, id)
 	if err != nil {
 		return 0, err
 	}
@@ -252,21 +243,16 @@ func (q *Queries) GetGame(ctx context.Context, arg GetGameParams) (GetGameRow, e
 const getPlatform = `-- name: GetPlatform :one
 SELECT id, name
 FROM platform
-WHERE id = $1 AND user_id = $2 AND deleted_at IS NULL
+WHERE id = $1 AND deleted_at IS NULL
 `
 
-type GetPlatformParams struct {
-	ID     uuid.UUID
-	UserID uuid.UUID
-}
-
 type GetPlatformRow struct {
 	ID   uuid.UUID
 	Name string
 }
 
-func (q *Queries) GetPlatform(ctx context.Context, arg GetPlatformParams) (GetPlatformRow, error) {
-	row := q.db.QueryRow(ctx, getPlatform, arg.ID, arg.UserID)
+func (q *Queries) GetPlatform(ctx context.Context, id uuid.UUID) (GetPlatformRow, error) {
+	row := q.db.QueryRow(ctx, getPlatform, id)
 	var i GetPlatformRow
 	err := row.Scan(&i.ID, &i.Name)
 	return i, err
@@ -406,7 +392,7 @@ func (q *Queries) ListGames(ctx context.Context, userID uuid.UUID) ([]ListGamesR
 const listPlatforms = `-- name: ListPlatforms :many
 SELECT id, name
 FROM platform
-WHERE user_id = $1 AND deleted_at IS NULL
+WHERE deleted_at IS NULL
 ORDER BY name
 `
 
@@ -415,8 +401,8 @@ type ListPlatformsRow struct {
 	Name string
 }
 
-func (q *Queries) ListPlatforms(ctx context.Context, userID uuid.UUID) ([]ListPlatformsRow, error) {
-	rows, err := q.db.Query(ctx, listPlatforms, userID)
+func (q *Queries) ListPlatforms(ctx context.Context) ([]ListPlatformsRow, error) {
+	rows, err := q.db.Query(ctx, listPlatforms)
 	if err != nil {
 		return nil, err
 	}
@@ -504,15 +490,14 @@ func (q *Queries) UpdateGame(ctx context.Context, arg UpdateGameParams) (UpdateG
 
 const updatePlatform = `-- name: UpdatePlatform :one
 UPDATE platform
-SET name = $3
-WHERE id = $1 AND user_id = $2 AND deleted_at IS NULL
+SET name = $2
+WHERE id = $1 AND deleted_at IS NULL
 RETURNING id, name
 `
 
 type UpdatePlatformParams struct {
-	ID     uuid.UUID
-	UserID uuid.UUID
-	Name   string
+	ID   uuid.UUID
+	Name string
 }
 
 type UpdatePlatformRow struct {
@@ -521,7 +506,7 @@ type UpdatePlatformRow struct {
 }
 
 func (q *Queries) UpdatePlatform(ctx context.Context, arg UpdatePlatformParams) (UpdatePlatformRow, error) {
-	row := q.db.QueryRow(ctx, updatePlatform, arg.ID, arg.UserID, arg.Name)
+	row := q.db.QueryRow(ctx, updatePlatform, arg.ID, arg.Name)
 	var i UpdatePlatformRow
 	err := row.Scan(&i.ID, &i.Name)
 	return i, err