feat(plan): /plan-options multi-angle best-of-N planning

[ryzizub]

Problem. /plan produces a single plan from one pre-chosen approach; there's no best-of-N.

Proposal. Fan out lens planners (simplicity, risk, speed, maintainability) in parallel → judge against the success criteria → AskUserQuestion to pick or merge. Larger build; do once the success-criteria gate is stable.

Acceptance criteria.

• N competing plans written to docs/plan/options/.
• Judge ranks against success criteria + NON-GOALS.
• Winner handed to /build.