merge: resolve conflicts with origin/main — keep improved colours and layout

fix: remove stale Gemini/ChromaDB refs, improve chart contrast, harden error handling

Stability: Fix duplicate Dash output error and add graceful Astra DB connection handling

fix: resolve runtime bugs, stale references, and config drift

fix: restore missing stats keys and update astrapy 2.x API

feat: migrate vector store from ChromaDB to Astra DB + Astra Vectorize

chore: add core/ modules, archive legacy code, update gitignore