Mixed proposal format — lump sum for some trades, detailed for others in one proposal

Allow mixing lump sum and detailed line-item formats within a single proposal, on a per-trade basis. For example: show plumbing as a lump sum total, but show carpentry with full line-item detail — all in the same client-facing proposal.

Currently proposals are either all detailed or all lump sum. Contractors need flexibility to hide detail on trades they sub out while showing detail on trades they self-perform.