fix(web): address code review findings from Razor Pages migration

- Remove legacy wwwroot files (old index.html, app.css, api.js, page scripts)
- Add Index page that redirects / to /board
- Fix mapping delete button missing handler=Delete in URL
- Add [IgnoreAntiforgeryToken] to AnalyticsModel for consistency
- Remove duplicate JS from _TaskDetail.cshtml (already in app.js)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

TaskTracker.Api/Pages/Partials/_MappingRow.cshtml

@@ -28,7 +28,7 @@
                 <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M17 3a2.85 2.85 0 1 1 4 4L7.5 20.5 2 22l1.5-5.5Z"/><path d="m15 5 4 4"/></svg>
             </button>
             <button class="btn btn--ghost btn--sm"
-                    hx-delete="/mappings?id=@Model.Id"
+                    hx-delete="/mappings?handler=Delete&id=@Model.Id"
                     hx-target="#mapping-row-@Model.Id"
                     hx-swap="outerHTML"
                     hx-confirm="Delete this mapping rule?"