fix(tasks): reclaim board height and make pagination readable

[witbrock]

All Tasks capped the board above the bottom of its details pane, leaving a large unused area, and the load-more button inherited white text on its white background. The board now stretches beside the inspector while retaining its scrollable viewport; pagination explicitly uses dark text and can wrap in narrow space. The existing bounded 50-task requests and append logic are unchanged.

Validation: 16 focused Jest tests passed (taskPanelLayout and taskPanelGroupFilters), node syntax and diff checks passed. Chromium using the real panel module and stylesheet with synthetic read-only API pages reproduced white-on-white text and a 2,832–2,979 px bottom gap on the baseline. The candidate eliminated that gap, kept cards scrollable, loaded 50 then 100 unique cards, showed disabled Loading… and No more tasks to load, and had no document overflow at 1920×1080, 1536×864 and 1280×900. The closed-pane layout was checked by hiding the inspector in the fixture: this UI currently always selects one. Screenshots and measurements are retained in the worker's .run/task-board-{baseline,candidate}/ directories. This is fixture rendering evidence, not live authenticated acceptance.

Merge decision changes — the Tier 1 evidence supports this scoped CSS repair; no blocking regression observed. No deployment requested by the task. Controller owns Von reporting/state updates.

Task: JVNAUTOSCI-2760 / #V#task_agent_e60306fb6a89c7a690a3ff2624442e5c