feat: Parse remap.layout_options extension in keyboard.json

[yoichiro]

Summary

Phase 1 of the runtime layout options work coordinated with the remap-qmk-module and remap-build-server sessions: the type definitions and validating parser for a new Remap-only extension field in QMK's keyboard.json.

• Adds RemapLayoutOptions / RemapLayoutVariant types under src/services/workbench/types/RemapLayoutOptions.ts, mirroring the exchanged spec (remap.layout_options.{labels, variants}).
• Adds parseRemapLayoutOptions() under src/services/workbench/RemapLayoutOptionsParser.ts. A missing remap.layout_options is a valid state and yields { success: true, data: null }; a present-but-broken field yields { success: false, errors: [...] } with a full list of human-readable errors.
• QMK ignores the unknown remap field, and remap-qmk-module will convert it into VIA-style layouts.labels + KLE-encoded layouts.keymap at firmware-build time. Client-side validation mirrors the invariants the converter enforces so any keyboard.json that the Form Editor accepts will convert cleanly server-side.
• Stacks on top of feat: Add Remap module toggle to keyboard.json form editor #927 (Remap module toggle). The next phases will surface this in the Form Editor UI and in the Visual Editor preview.

Invariants enforced by the parser

• One-element labels (e.g. ["Split Backspace"]) is the implicit Off/On idiom. Two-element labels are ambiguous and are rejected up-front so a well-defined mapping to VIA JSON is always possible.
• variants[].option must index into labels.
• variants[].choice must fit that option's choice count (two for a one-element label, labels[option].length - 1 for an explicit multi-choice label).
• Every required (option, choice) pair must be covered by at least one variant.
• A matrix cell cannot appear both in the default layout keys and in variants, and cannot repeat within the same (option, choice).
• The optional layoutDefaultKeys input drives the LAYOUT-vs-variants matrix-collision check; callers that only want to validate the remap section in isolation can omit it.

Test plan

• npm run type-check passes.
• npm run lint — no new errors from the touched files.
• npm test -- --run — all tests pass (1237 total).
• npm test -- RemapLayoutOptionsParser.test.ts --run — 24 targeted cases pass, covering: absence handling (null / non-object inputs), a minimal Split Backspace layout, implicit Off/On labels, an explicit three-choice layout, optional key fields (w, h, r, rx, ry) round-trip, two-element label rejection, empty label / non-array label rejection, empty variants rejection, empty variants[].keys rejection, out-of-range option / choice, malformed matrix / missing x/y, missing choice coverage (implicit and explicit), matrix collision with LAYOUT_default, (option, choice, matrix) duplication within variants, same matrix allowed across different (option, choice) pairs, and the LAYOUT cross-check being skipped when layoutDefaultKeys is omitted.