build(aircraft): validate the configs before publishing them

[nabeelio]

Aircraft configs used to be TypeScript classes, so the compiler caught a typo'd feature name or a missing field. As JSON they have nothing in front of them, and a broken document publishes to every VA and then fails quietly - the client skips a feature key it doesn't recognise and logs a warning nobody reads.

• The check lives in the bundle task rather than behind a test runner. This repo has none, and adding vitest plus config to validate 36 JSON files is a lot of machinery for something the build already walks. CI runs npm run build, so a bad document now fails there instead of shipping.
• Validates meta's required fields, that sim is one the client understands, that meta.id is unique across documents, that match is an array, and that every features/disabled key exists in this repo's AircraftFeature enum. Problems are collected rather than thrown one at a time, so one build reports all of them.
• The vocabulary is parsed out of defs.ts instead of imported, because the gulpfile runs before any TypeScript is compiled and defs.js is a build artifact that can lag its source. Parsing zero members throws rather than returning an empty set, which would quietly turn every check into a no-op.
• Restores coverage that moving the library here removed. The plugin's corpus.test.ts used to validate all 35 documents against the engine on every CI run; it now guards the four examples that stayed behind, and nothing was checking these.

Verified against the real corpus: a clean build passes all 36, and each failure mode was injected and confirmed to fail the build with the offending file named - typo'd feature key, unknown sim, missing meta.author, duplicate meta.id, non-array match, non-object disabled.