feat(chat): multi-turn Chat Session with Conversation history sidebar

Grounded Ask owns the product chat UI: persistent thread_id across a
Chat Session, New chat / Continue conversation, and a sidebar that lists
Conversations from the Conversation Record with formatted run metadata
(timing, tokens, evidence chunks).

Co-authored-by: Cursor <cursoragent@cursor.com>

.streamlit/config.toml

@@ -0,0 +1,11 @@
+[server]
+headless = true
+port = 8502
+
+[theme]
+base = "light"
+primaryColor = "#2f5d9f"
+backgroundColor = "#eef3f7"
+secondaryBackgroundColor = "#f7f9fb"
+textColor = "#0c1a2a"
+font = "sans serif"