Work areas without scope display helpfully in estimates

Non-scoped work areas now show hints instead of disappearing, and General items always calculate.

Bug Fixes

Work areas that don't have any scope notes, materials, or custom materials would previously disappear from the estimate, making it hard to tell what was set up. Now they display with a "No scope — add scope to estimate this work area" hint, and General line items (project-wide charges like equipment and mobilization) are always calculated correctly even when all work areas are empty.

We also renamed "Job Level" items to "General" for clarity — these apply across the entire estimate, not to individual work areas.