Add authentication, authorization, and team-scoped access control

Implement email/password auth with JWT sessions and API key auth for
sandbox lifecycle. Users get a default team on signup; sandboxes,
snapshots, and API keys are scoped to teams.

- Add user, team, users_teams, and team_api_keys tables (goose migrations)
- Add JWT middleware (Bearer token) for user management endpoints
- Add API key middleware (X-API-Key header, SHA-256 hashed) for sandbox ops
- Add signup/login handlers with transactional user+team creation
- Add API key CRUD endpoints (create/list/delete)
- Replace owner_id with team_id on sandboxes and templates
- Update all handlers to use team-scoped queries
- Add godotenv for .env file loading
- Update OpenAPI spec and test UI with auth flows

internal/api/handlers_files.go

@@ -9,6 +9,7 @@ import (
 	"connectrpc.com/connect"
 	"github.com/go-chi/chi/v5"
 
+	"git.omukk.dev/wrenn/sandbox/internal/auth"
 	"git.omukk.dev/wrenn/sandbox/internal/db"
 	pb "git.omukk.dev/wrenn/sandbox/proto/hostagent/gen"
 	"git.omukk.dev/wrenn/sandbox/proto/hostagent/gen/hostagentv1connect"
@@ -30,8 +31,9 @@ func newFilesHandler(db *db.Queries, agent hostagentv1connect.HostAgentServiceCl
 func (h *filesHandler) Upload(w http.ResponseWriter, r *http.Request) {
 	sandboxID := chi.URLParam(r, "id")
 	ctx := r.Context()
+	ac := auth.MustFromContext(ctx)
 
-	sb, err := h.db.GetSandbox(ctx, sandboxID)
+	sb, err := h.db.GetSandboxByTeam(ctx, db.GetSandboxByTeamParams{ID: sandboxID, TeamID: ac.TeamID})
 	if err != nil {
 		writeError(w, http.StatusNotFound, "not_found", "sandbox not found")
 		return
@@ -95,8 +97,9 @@ type readFileRequest struct {
 func (h *filesHandler) Download(w http.ResponseWriter, r *http.Request) {
 	sandboxID := chi.URLParam(r, "id")
 	ctx := r.Context()
+	ac := auth.MustFromContext(ctx)
 
-	sb, err := h.db.GetSandbox(ctx, sandboxID)
+	sb, err := h.db.GetSandboxByTeam(ctx, db.GetSandboxByTeamParams{ID: sandboxID, TeamID: ac.TeamID})
 	if err != nil {
 		writeError(w, http.StatusNotFound, "not_found", "sandbox not found")
 		return