feat(engy): add engy sync module

[roykollensvendsen]

Summary

Adds a sync module for engy, the provider added in #5910. That PR was split so the provider could land first, and this is the module that was taken out of it. One change since then: the module now keeps every authored field and overwrites only the cost, context and modalities, as the Mistral module does. Before, it rebuilt each model from a fixed field list, which would have stripped v2's new type field on the next run.

engy publishes prices, the context window and modalities on a public GET https://api.engy.ai/v1/models (no auth). The module keeps those current. While #5910 was open it caught two real changes: kimi-k3's 30% price rise on 09-03 and qwen3.8-27b's larger window on 09-13.

What it writes and what it leaves alone

• Writes the cost (input, output, cache_read), limit.context and modalities.
• Leaves everything else as authored: the input/output split, reasoning_options, interleaved, any other cost keys, provider, experimental and status. The public list gives only the context window, which on engy is max_input + max_output, so the module never derives the split from it.
• base_model: an authored base_model wins over the slug resolver.
• Modalities: an absent list keeps what the file says. A context_length of 0 or less counts as unreported.
• skipCreates: a new id opens a [missing-model] issue instead of a file, because a created file would ship limit.output = 0. Today the list and the catalogue match, so the first run opens nothing.
• deleteMissing: false: {"data":[]} passes the schema, so retired ids are reported, not deleted.
• Prices are rounded to six decimals, so the hourly run is a no-op when nothing has changed.

The module is registered in sync/index.ts (alphabetical, direct group), with an engy:sync script and an engy Notes section in sync.md. It is not on REVIEWED_REASONING_PROVIDERS.

Test plan

• packages/core/test/engy.test.ts: 18 pass. The carry-through test now covers type and reasoning_options and fails on the old field list. The suite reads the shipped engy files and asserts that a sync round trip leaves them unchanged.
• bun models:sync engy --dry-run, then a real run, then --dry-run again, 2026-10-07: 8 unchanged each time, no files touched
• bun validate
• bun run test in packages/sdk: 25 pass
• tsc --noEmit in packages/core: the same 78 errors as on dev, none of them in engy code
• Based on dev 25bd6dc

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