feat(webapp): add session persistence via URL hash routing + sessionStorage

- app.js: hash-based router (#runs / #new / #profiles / #report/{runId})
  - navigate() pushes history entries for back/forward support
  - _restoreSession() reads hash on load and popstate
  - sessionStorage fallback for same-tab refreshes
  - run-card highlights selected run (.run-card.selected)
- runner.js: use App.navigate() for report redirect; persist lastRunId to sessionStorage
- index.html: report nav button starts disabled (enabled on run select/restore)
- app.css: .run-card.selected with petrol border + ring

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

webapp/static/index.html

@@ -22,7 +22,7 @@
         <button class="nav-item" data-view="new">
           <span class="nav-ico">＋</span><span>新建评估</span>
         </button>
-        <button class="nav-item" data-view="report" data-requires-run="1">
+        <button class="nav-item" data-view="report" data-requires-run="1" disabled>
           <span class="nav-ico">▤</span><span>报告详情</span>
         </button>
         <button class="nav-item" data-view="profiles">