Add instant bilingual settings and verify business flows

[Jeffreyliu0131]

The workspace previously exposed Chinese-only UI and required a separate save action for follow-up settings. This adds Chinese/English display preferences that apply immediately and persist across reloads and tabs, plus version-aware automatic saving of the check interval in the existing visual style.

Localization covers navigation, tasks, work items, forecasts, charts, documents, quotes, errors and exports. Original user content and evidence remain unchanged, CNY and integer-money values are preserved, and quote CSV import accepts Chinese or English headers. Agent responses no longer have a fixed Chinese-only prompt; English restocking and evidence requests retain tool-read requirements.

Acceptance review also fixed accidental translation of original values, ambiguous CSV columns, export formula handling, and uncertain schedule-save recovery. Purchase approval remains explicit and independent of settings.

Validation:

• 64 production-frontend cases passed, zero failures/skips/flaky results.
• 415 backend/API/PostgreSQL cases passed, including three real HTTP/browser chains.
• Real English approval produced one 40-unit purchase after a double click: cash 1000 → 600 CNY, on-hand 20, in-transit 40. Language changes/reloads preserved state; changing a paused schedule did not resume it.
• Typecheck, production build, API contract, 1,334-entry locale audit, formatting and Ruff passed. Committed source hashes match the tested files.
• Development database content hashes remained unchanged across 37 tables.

Evidence and reproducible scope: docs/reports/i18n-settings-verification.md and its JSON companion. Suppliers used a deterministic test adapter; no paid model or real-supplier validation was performed. No daily deployment or development-database migration is included. The existing ECharts chunk-size warning remains; lazy loading is verified.