Offline PWA: one-question-per-page wizard engine

[rec3141]

Part of #1.

The core wizard interaction. Questions built from the active MIxS combination via the existing organizeForm() (src/lib/mixs/sample-form.ts) — no new field registry.

Interaction spec

• One input per page. State: mainQueue[], skipped[] (FIFO), answers{}, cursor.
• Action button reads Skip while empty/invalid; flips to Next the instant the value is non-empty and valid ($derived validity from the slot's MIxS type/pattern).
• Skip → push key to skipped[], advance. Next → commit, advance.
• After mainQueue drains, re-present skipped[] as a second pass; second-pass Skip = leave blank, advances without re-queuing (loop terminator).
• Complete always present → validate required-only → jump to first unanswered required, else review screen (answers + blanks/skips highlighted, tap to edit) → finalize.
• Header progress Q n / N · k skipped, plus Back.
• Sticky carry-forward: project/site/date+time/weather/people/env_medium captured once per burst (wizard-shaped fillRight/applyFirstToEmpty).

Done when

• A full sample can be captured by tapping Next/Skip through the queue, skips loop back, and Complete enforces required fields.