fix(chat): preserve category collapse from Recent

[wtj-0527]

Summary

• treat Recent as a shortcut when selecting a session
• preserve the saved collapsed state of the session's real category
• keep existing category auto-reveal behavior for direct URLs, refreshes, and ordinary navigation
• keep modified-click/new-window routing unchanged

Root cause

The active-session watcher auto-expanded the active session's real category without knowing whether the selection originated from the Recent shortcut. As a result, selecting a Recent item overwrote the user's collapsed category state and rendered the same active session in both places.

Tests

• Added a regression E2E that failed before the fix because Project Alpha appeared twice after selection (expected 1, received 2).
• NODE_ENV=test npx playwright test tests/e2e/session-categories.spec.ts — 9 passed
• NODE_ENV=test npx vitest run tests/client/session-category-groups.test.ts — 5 passed
• NODE_ENV=development npm run harness:check — passed
• NODE_ENV=development npm run build — passed

Closes #2741

This PR is intentionally left unmerged pending LPK installation acceptance.

[wtj-0527]

Installation-acceptance candidate is ready.

• Runtime image: registry.cn-shanghai.aliyuncs.com/wtjking/hermes-web-ui:v0.6.47-pr2742-16538e08-202608261605
• Image digest: sha256:234dfc38866d0269bd116b46a37b6168f5c79c1aebab362c9394d8d080d69aad
• LazyCat wrapper PR: test: package Recent category-collapse fix 2026.08.26.1612 wtj-0527/lazycat-hermes-studio#104
• LPK version: 2026.08.26.1612
• LPK SHA256: 28fc08bf9c9b97a930e4aec2459dfaa81b3caedb378b9367eeb4a73f22bb479c

No PR was merged and no package was installed or deployed.