What does this PR do?

Makes the Kanban dashboard request the selected board explicitly even when the selected slug is default. Previously some dashboard REST calls omitted board=default, allowing the backend's current-board pointer to leak a non-default board into the UI while the selector still showed Default.

Related Issue

Fixes #21819

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✅ Tests (adding or improving test coverage)

Changes Made

• plugins/kanban/dashboard/dist/index.js: route config and boards requests through withBoard(..., board) and include board in the create-board callback dependencies.
• tests/plugins/test_kanban_dashboard_plugin.py: verify the backend accepts board=default and add a static regression test that dashboard code explicitly uses withBoard(..., board) for default-sensitive requests.

How to Test

1. python3 -m pytest tests/plugins/test_kanban_dashboard_plugin.py -k 'explicit_board_default_param or dashboard_requests_default_board_explicitly' -o 'addopts=' --tb=short -q
2. Fail-without-fix proof: with the dashboard dist change reverted, test_dashboard_requests_default_board_explicitly fails.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes
• I've tested on my platform: Linux / Python 3.11

Documentation & Housekeeping

• I've updated relevant documentation — N/A
• I've updated cli-config.yaml.example — N/A
• I've updated CONTRIBUTING.md or AGENTS.md — N/A
• I've considered cross-platform impact — dashboard JS/API requests only
• I've updated tool descriptions/schemas — N/A