feat(modules): RequireModule middleware to gate route groups

Add RequireModule middleware that returns 404 with
{"error":"module '<id>' is not enabled"} when a module is disabled.

Wrap route groups:
- projects → RequireModule("projects")
- audit → RequireModule("audit")
- integrations/odoo → RequireModule("odoo")
- jobs, job-definitions, runners → RequireModule("jobs")
- /api/runner (runner-facing) → RequireModule("jobs")
- dag → RequireModule("dag") (extracted into sub-route)

Ref #98

internal/api/middleware.go

@@ -183,6 +183,22 @@ func (s *Server) RequireRunnerAuth(next http.Handler) http.Handler {
 	})
 }
 
+// RequireModule returns middleware that rejects requests with 404 when
+// the named module is not enabled.
+func (s *Server) RequireModule(id string) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if !s.modules.IsEnabled(id) {
+				w.Header().Set("Content-Type", "application/json")
+				w.WriteHeader(http.StatusNotFound)
+				w.Write([]byte(`{"error":"module '` + id + `' is not enabled"}`))
+				return
+			}
+			next.ServeHTTP(w, r)
+		})
+	}
+}
+
 func extractBearerToken(r *http.Request) string {
 	h := r.Header.Get("Authorization")
 	if strings.HasPrefix(h, "Bearer ") {

internal/api/routes.go

@@ -101,6 +101,7 @@ func NewRouter(server *Server, logger zerolog.Logger) http.Handler {
 
 		// Projects (read: viewer, write: editor)
 		r.Route("/projects", func(r chi.Router) {
+			r.Use(server.RequireModule("projects"))
 			r.Get("/", server.HandleListProjects)
 			r.Get("/{code}", server.HandleGetProject)
 			r.Get("/{code}/items", server.HandleGetProjectItems)
@@ -150,10 +151,20 @@ func NewRouter(server *Server, logger zerolog.Logger) http.Handler {
 				r.Get("/bom/export.csv", server.HandleExportBOMCSV)
 				r.Get("/bom/export.ods", server.HandleExportBOMODS)
 
-				// DAG (read: viewer, write: editor)
+				// DAG (gated by dag module)
-				r.Get("/dag", server.HandleGetDAG)
+				r.Route("/dag", func(r chi.Router) {
-				r.Get("/dag/forward-cone/{nodeKey}", server.HandleGetForwardCone)
+					r.Use(server.RequireModule("dag"))
-				r.Get("/dag/dirty", server.HandleGetDirtySubgraph)
+					r.Get("/", server.HandleGetDAG)
+					r.Get("/forward-cone/{nodeKey}", server.HandleGetForwardCone)
+					r.Get("/dirty", server.HandleGetDirtySubgraph)
+
+					r.Group(func(r chi.Router) {
+						r.Use(server.RequireWritable)
+						r.Use(server.RequireRole(auth.RoleEditor))
+						r.Put("/", server.HandleSyncDAG)
+						r.Post("/mark-dirty/{nodeKey}", server.HandleMarkDirty)
+					})
+				})
 
 				r.Group(func(r chi.Router) {
 					r.Use(server.RequireWritable)
@@ -174,20 +185,20 @@ func NewRouter(server *Server, logger zerolog.Logger) http.Handler {
 					r.Post("/bom/merge", server.HandleMergeBOM)
 					r.Put("/bom/{childPartNumber}", server.HandleUpdateBOMEntry)
 					r.Delete("/bom/{childPartNumber}", server.HandleDeleteBOMEntry)
-					r.Put("/dag", server.HandleSyncDAG)
-					r.Post("/dag/mark-dirty/{nodeKey}", server.HandleMarkDirty)
 				})
 			})
 		})
 
 		// Audit (read-only, viewer role)
 		r.Route("/audit", func(r chi.Router) {
+			r.Use(server.RequireModule("audit"))
 			r.Get("/completeness", server.HandleAuditCompleteness)
 			r.Get("/completeness/{partNumber}", server.HandleAuditItemDetail)
 		})
 
 		// Integrations (read: viewer, write: editor)
 		r.Route("/integrations/odoo", func(r chi.Router) {
+			r.Use(server.RequireModule("odoo"))
 			r.Get("/config", server.HandleGetOdooConfig)
 			r.Get("/sync-log", server.HandleGetOdooSyncLog)
 
@@ -210,6 +221,7 @@ func NewRouter(server *Server, logger zerolog.Logger) http.Handler {
 
 		// Jobs (read: viewer, write: editor)
 		r.Route("/jobs", func(r chi.Router) {
+			r.Use(server.RequireModule("jobs"))
 			r.Get("/", server.HandleListJobs)
 			r.Get("/{jobID}", server.HandleGetJob)
 			r.Get("/{jobID}/logs", server.HandleGetJobLogs)
@@ -224,6 +236,7 @@ func NewRouter(server *Server, logger zerolog.Logger) http.Handler {
 
 		// Job definitions (read: viewer, reload: admin)
 		r.Route("/job-definitions", func(r chi.Router) {
+			r.Use(server.RequireModule("jobs"))
 			r.Get("/", server.HandleListJobDefinitions)
 			r.Get("/{name}", server.HandleGetJobDefinition)
 
@@ -235,6 +248,7 @@ func NewRouter(server *Server, logger zerolog.Logger) http.Handler {
 
 		// Runners (admin)
 		r.Route("/runners", func(r chi.Router) {
+			r.Use(server.RequireModule("jobs"))
 			r.Use(server.RequireRole(auth.RoleAdmin))
 			r.Get("/", server.HandleListRunners)
 			r.Post("/", server.HandleRegisterRunner)
@@ -251,6 +265,7 @@ func NewRouter(server *Server, logger zerolog.Logger) http.Handler {
 
 	// Runner-facing API (runner token auth, not user auth)
 	r.Route("/api/runner", func(r chi.Router) {
+		r.Use(server.RequireModule("jobs"))
 		r.Use(server.RequireRunnerAuth)
 		r.Post("/heartbeat", server.HandleRunnerHeartbeat)
 		r.Post("/claim", server.HandleRunnerClaim)