Rewrite workshop 02: Optics and frames #329

Part of #326.

Questions

• Generic optics as the base: sensor size, focal length, focal reducer, orientation; anamorphic squeeze?
• Rig as an optional saved bundle on top (body, lens set, vignetting)
• Snapshot vs. live reference (today FOV reads the snapshot, vignetting the live rig)
• Frame derived from optics vs. free crop

As-is sources

packages/fov-math, presets, framings, packages/vocab/src/framing.ts, docs/features/rig-explorer.md

Format

No product code. I prepare docs/rewrite/02-optics.md with the as-is state (with file paths), the problems and leaks, a proposal and the open questions; mockups go to docs/rewrite/mockups/. The owner decides, the decisions are recorded in the page's "Decided" section and here, and the PR is merged into rewrite/plan.