Harden strategy switch console boot fetch timeout fallback

[Pigbibi]

Why

The console can stay stuck during initialization when backend bootstrap APIs (/api/session, /api/strategy-profiles, /api/config) do not return.

What changed

• Add request timeout wrapper (15s) for startup API calls
• Add explicit JSON/error handling helper
• On bootstrap config failure, degrade gracefully to public preview mode instead of hanging on loading state
• Add new bootTimeout message in Chinese/English
• Guard boot() with top-level fallback to avoid uncaught boot exception

How to verify

• node --test tests/strategy_switch_worker_validation.mjs
• node --check web/strategy-switch-console/app.js
• node --check web/strategy-switch-console/app_js.js
• node --check web/strategy-switch-console/worker.js

[github-actions]

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