refactor(spectre): reorganize AI/streaming logic, improve type-safety…

…, and clean up UI/helpers

- Move instructions, request, generation, streaming, error utils and quota tracker into modular node files
- Improve quota management and pacing via SpectreAiQuotaTracker
- Modularize and simplify streaming consumption and retry logic with clearer retry decisions
- Strengthen typing and normalize helper APIs across UI, board, and upload modules
- Fix sketch editor argument handling and loop detector signature helpers
- Enhance upload error classification and regex handling; add safer patterns and context helpers
- Various minor cleanups, performance and safety fixes (inactivity monitor, sanitize for logging)

Add AI screenshots and update README