Modernize frontend, modularize routers, and improve logging reliability

[NikkeTryHard]

This PR brings the fork up to date with several improvements spanning logging, reliability, and architecture.

Logging Improvements

• Remove nested log calls and leading spaces for cleaner output
• Add new logging tags for better categorization
• Silence verbose modules that cluttered logs
• Expand test coverage for logging behavior

Reliability Fixes

• Improve chat message input and submission reliability in page controller
• Better handling of transitional UI states

Architecture Refactoring

• Deprecate and remove legacy JS/CSS frontend (24 files)
• Add React SPA with Vite, TypeScript, and Vitest
• Extract routers into focused modules: auth_files, helper, model_capabilities, ports, proxy, server
• Add frontend_build launcher module
• Split DEFAULT_THINKING_LEVEL into model-specific configs (PRO/FLASH)
• Improve error handling and debug snapshot saving
• Expand test coverage across all modified modules