fix: board picker uses index into re-fetched list (race condition)

[nickmeinhold]

Problem

In src/bot/callbacks/newtask-flow.ts, the board selection callback (handleNewTaskBoardCallback) re-fetches the full board list from the API and uses the button's index to resolve which board was selected:

const boards = await client.getBoards(flow.workspacePublicId);
const board = boards[boardIdx];

If a board is added, removed, or reordered between when the picker was rendered and when the user clicks a button, the index may point to the wrong board.

Proposed Fix

Store the board mapping (publicId + name) in the flow object when the picker is first rendered, similar to how lists are already stored:

flow.boards = boards.map(b => ({ publicId: b.publicId, name: b.name }));

Then resolve from flow.boards[boardIdx] in the callback instead of re-fetching.

Context

Flagged during cage-match review of PR #13 by KelvinBitBrawler.