Add categories to page render context

- Add post IDs to tech blog index template

src/MyWebLog/Handlers/Post.fs

@@ -193,6 +193,7 @@ let home : HttpHandler = fun next ctx -> task {
             return!
                 Hash.FromAnonymousObject {|
                     page       = DisplayPage.fromPage webLog page
+                    categories = CategoryCache.get ctx
                     page_title = page.title
                     is_home    = true
                 |}

src/MyWebLog/Handlers/Routes.fs

@@ -41,6 +41,7 @@ module CatchAll =
                 yield fun next ctx ->
                     Hash.FromAnonymousObject {|
                         page       = DisplayPage.fromPage webLog page
+                        categories = CategoryCache.get ctx
                         page_title = page.title
                         is_page    = true
                     |}