feat: add workspace and global session navigation

[section2014]

Summary

• Add workspace/global session navigation with global running-session aggregation and searchable history.
• Preserve cross-project session selection, session completion indicators, file explorer synchronization, and mobile accessibility behavior.
• Make workspace and global session rows use the full available width, with consistent floating rename/delete controls.
• Add regression coverage for navigation, running-session state, history search, session-row layout, and control styling.

Validation

• node --test app/api/agent/running/route.test.mjs app/api/sessions/[id]/route.test.mjs components/FileExplorer.test.mjs components/SessionSidebar.test.mjs hooks/useAgentSession.test.mjs lib/global-history.test.mjs lib/rpc-manager-running.test.mjs lib/running-sessions.test.mjs — 54 passed
• node_modules/.bin/tsc --noEmit — passed
• npm run lint — passed

npm test still reports 19 failures in this Windows environment: component SSR tests invoke useI18n without an I18nProvider, and two directory-browser tests depend on symlink permissions/POSIX path behavior. The targeted feature suite above passes.

[section2014]

[section2014]

工作区基本保持不变