delete the batch practice-problems module (superseded by practice sessions)

Owner ruling 2026-10-04: the module is a sunk cost, retrievable from
history if ever revisited. Removed: core practice contracts + pipeline
helpers, the PracticeStore port + adapter + data dir path, server
service + API routes (sets, clusters picker, practice aborts), the
practice pages + dialog/exam/list UI, chain-table's Generate handoff,
sidebar nav, activity-dock practice rows, and the partitioner/
problemGenerator/grader model roles (BACKGROUND_MODEL_ROLES 8 → 5).

Survivors, moved to core/chains.ts (pure + browser-safe): ReasoningChain,
chainsForSelection, formatChainLine — the chain table and graph
emission still consume them.

src/server/index.ts

@@ -7,7 +7,6 @@
 export * from "./chat-handler.ts";
 export * from "./events-stream.ts";
 export * from "./chats.ts";
-export * from "./practice.ts";
 export * from "./graph.ts";
 export * from "./commit-positions.ts";
 export * from "./jobs.ts";