feat(httputil): add Bind/BindEmpty request binding from path and query; v1.6.0

Bind and BindEmpty fill Req from path/query/json struct tags and validate
once, extending the typed decode->validate->call->encode pipeline to routes
with identifiers and filters. Conversion via builtins + encoding.TextUnmarshaler
(uuid.UUID, time.Time); malformed value -> 400 naming the parameter; default:
applies only when absent; repeated query -> slice; mis-tagged struct panics at
wiring. Purely additive; existing adapters unchanged. Coordinated lockstep v1.6.0.

httputil/doc.go

@@ -22,6 +22,26 @@
 //	    return CreateUserRes{ID: u.ID}, nil
 //	}))
 //
+// # Request binding
+//
+// [Bind] and [BindEmpty] extend the same decode → validate → call → encode pipeline
+// to requests that carry more than a JSON body. Each field declares its source with
+// a struct tag — path:, query: or json: — and the assembled struct is validated once:
+//
+//	type getRoleReq struct {
+//	    RoleID uuid.UUID `path:"roleID"  validate:"required"`
+//	    Expand []string  `query:"expand"`
+//	}
+//
+//	r.Get("/roles/{roleID}", httputil.Bind(v, logger, func(ctx context.Context, req getRoleReq) (RoleRes, error) {
+//	    return svc.GetRole(ctx, req.RoleID)
+//	}))
+//
+// A malformed value is a 400 naming the parameter (never a 500), uuid.UUID and
+// time.Time bind via [encoding.TextUnmarshaler], and a mis-tagged struct fails at
+// wiring rather than on a request. Use these instead of [HandlerFunc] for any route
+// with an identifier or a filter.
+//
 // # Centralized error handler
 //
 // [Error] is the single point of error processing for all handlers:
@@ -29,16 +49,16 @@
 //   - 4xx → Warn level   (client mistake — not a server failure)
 //   - 499 → Info level   (client cancelled the request intentionally)
 //
-// Call it directly from [HandlerFunc] when you need path parameters or custom logic:
+// Call it directly from [HandlerFunc] for genuinely custom responses — streaming,
+// file downloads, non-JSON content types:
 //
-//	r.Get("/users/{id}", httputil.HandlerFunc(func(w http.ResponseWriter, r *http.Request) error {
-//	    id := chi.URLParam(r, "id")
-//	    u, err := svc.GetUser(r.Context(), id)
+//	r.Get("/reports/{id}.csv", httputil.HandlerFunc(func(w http.ResponseWriter, r *http.Request) error {
+//	    rows, err := svc.Export(r.Context(), chi.URLParam(r, "id"))
 //	    if err != nil {
 //	        httputil.Error(logger, w, r, err)
 //	        return nil
 //	    }
-//	    httputil.JSON(w, http.StatusOK, u)
-//	    return nil
+//	    w.Header().Set("Content-Type", "text/csv")
+//	    return csv.NewWriter(w).WriteAll(rows)
 //	}).ServeHTTP)
 package httputil