docs: update architecture and features for calendar + RAG scoping
- architecture.md: add Event model, services/events.py, routes/events.py,
CalendarView.vue, EventSlideOver.vue; update Conversation and Project
data model tables with new columns; update RAG Pipeline section with
three-value scope system, search_projects/set_rag_scope tools, and
project summary background job; fix dead-code note for models/event.py;
update execute_tool() signature docs; add services/projects.py entry
- features.md: replace CalDAV section with full Calendar section covering
internal store, AI tools, HomeView widget, and optional CalDAV sync;
update AI Chat scope chip description; remove done "Calendar view" item
from roadmap
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>