refactor(kanban): compose page with hemplate

Replace board page placeholder string replacement for options/board content with a hemplate page view and partial-rendered options. Cover page structure with DOM-aware scraper assertions.

req: html_safety/002

req: view/001

req: test/005

examples/kanban/templates/board.heml

@@ -3,13 +3,13 @@
     <h1>slhx Kanban</h1>
     <form data-slhx-handle="create_card" data-slhx-form="create_card" data-slhx-disable-while-pending>
       <input name="title" type="text" required="required" placeholder="Card title">
-      <select name="column" required="required">__OPTIONS__</select>
+      <select name="column" required="required">{+= self.options =+}</select>
       <button type="submit">Add card</button>
     </form>
     <p data-slhx-slot="notice">Ready</p>
   </header>
 
-  <div data-slhx-slot="board">__BOARD__</div>
+  <div data-slhx-slot="board">{+= self.board =+}</div>
   <aside data-slhx-slot="presence">Waiting for presence…</aside>
 
   <button type="button" data-slhx-handle="move_left" hidden="hidden">Move left</button>

examples/kanban/templates/partials/column_option.heml

@@ -0,0 +1 @@
+<option +value="self.id">{+ self.title +}</option>

examples/kanban/templates/partials/column_options.heml

@@ -0,0 +1,3 @@
+<template h-for="option in &self.options">
+  {+ option +}
+</template>