Add full English language support (i18n) across frontend and backend

[AbdulrahmanMasoud]

Summary

• Added complete English language support to MiroFish with vue-i18n on the frontend and bilingual API messages + LLM prompts on the backend
• English is now the default language with a toggle to switch to Chinese
• All LLM-generated output (reports, agent profiles, ontologies) adapts to the selected language

Changes

Frontend (13 Vue files + 4 new files):

• Installed vue-i18n with en.json and zh.json locale files (~180 translation keys)
• Created LanguageSwitcher component (EN/ZH toggle in navbar)
• Replaced all hardcoded Chinese strings with $t() calls across all views and components
• Added Accept-Language header to all API requests via axios interceptor

Backend API (5 files):

• Created utils/messages.py with bilingual message dictionary and msg() helper
• Added language field to Project model
• Replaced Chinese response strings in graph.py, report.py, simulation.py with msg() calls

Backend LLM Prompts (5 service files):

• Added English prompt versions for ontology_generator, oasis_profile_generator, report_agent, simulation_config_generator, zep_tools
• Added language parameter to all service constructors — prompts selected based on user's language preference
• Reports, agent profiles, and simulation output are generated in the user's chosen language

Test plan

• Start dev server (npm run dev), verify UI shows in English by default
• Toggle to Chinese and back — all labels, buttons, status badges, log messages switch
• Create a project in English mode — verify ontology, agent profiles, and reports generate in English
• Create a project in Chinese mode — verify everything still works as before
• Verify language preference persists across page refresh (localStorage)

[666ghj]

The project already has i18n support in place — please refer to [PR #428] for reference.