BACK-536 - Add wrapNavigationToSearch config to opt out of the boundary search handoff

[kossakovsky]

Summary

In the TUI, pressing j on the last row or k on the first row (or k at the top of the focused detail pane) hands focus to the search input. The wrap is deliberate (back-399), but it surprises vim-style navigation: j/k are expected to stay inside the list, and / and Ctrl+F already focus search directly.

This adds an opt-out config key that keeps today's behavior by default:

• wrapNavigationToSearch (boolean, default true), available through backlog config get/set/list and documented in ADVANCED-CONFIG.md
• when false, the handoff stops in the task list, the detail pane, and the kanban board (including empty columns)
• with the handoff disabled, boundary navigation falls back to the circular wrap both views used before back-399 (introduced in task-248)

Related Issue or Task

Closes #768

Backlog task: BACK-536

Task Checklist

• I have created a corresponding task in backlog/tasks/
• The task has clear acceptance criteria
• I have added an implementation plan to the task
• All acceptance criteria in the task are marked as completed

Testing

• bunx tsc --noEmit — passed
• bun run check . — passed (323 files)
• bun test — 1670 passed + 2 intentional skips / 0 failed (187 files)
• new coverage: wrap-disabled cases in task-viewer-boundary-navigation.test.ts, resolveBoardBoundaryToSearch cases in board-ui.test.ts, and a config get/set/list round-trip for the new key