Add soft delete + trash, keyboard-first web overhaul, move chapter tags to bottom

Adds SoftDelete/Trash across characters, chapters, locations, beats with a
purge schedule and Trash page. Reworks the web client for keyboard-driven
navigation (focus helpers, help overlay, keyboard.md doc). Moves the
ChapterPage tag editor to the bottom of the page to match CharacterDetailPage.

tests/Novelly.Api.Tests/CharacterArcTests.cs

@@ -152,7 +152,7 @@ public class CharacterArcTests : ServiceTestFixture
     }
 
     [Test]
-    public async Task Deleting_a_chapter_unpins_an_arc_stage_rather_than_deleting_it()
+    public async Task Trashing_a_chapter_hides_it_from_an_arc_stage_without_unpinning_it()
     {
         var chapter = await Chapters.CreateAsync(_novelId, new CreateChapterRequest("Landfall"));
         var stage = await Arcs.CreateAsync(
@@ -161,11 +161,14 @@ public class CharacterArcTests : ServiceTestFixture
         await Chapters.DeleteAsync(chapter.Id);
 
         var survivor = (await Arcs.GetAsync(stage.Id))!;
+        var response = survivor.ToResponse();
 
         Assert.Multiple(() =>
         {
-            Assert.That(survivor.ChapterId, Is.Null);
-            Assert.That(survivor.Title, Is.EqualTo("The map is wrong"));
+            Assert.That(survivor.ChapterId, Is.EqualTo(chapter.Id), "the pin survives so restoring the chapter restores the link");
+            Assert.That(response.ChapterNumber, Is.Null);
+            Assert.That(response.ChapterTitle, Is.Null);
+            Assert.That(response.Title, Is.EqualTo("The map is wrong"));
         });
     }