fix(plugin): add V1 default export descriptor to stop legacy loader probing every helper

[Futuri-Risk]

Fixes #86.

What

Adds a V1 plugin descriptor as the default export of index.js (and the rebuilt dist/llm-proxy.js):

export default { id: "opencode-llm-proxy", server: OpenAIProxyPlugin }

All 28 named exports stay untouched, so direct imports and the test suite are unaffected.

Why

Without a default export, opencode's loader takes the legacy path (getLegacyPlugins), which invokes every function-typed export as if it were the plugin factory. The pure helpers (buildPrompt, mapFinishReason, …) throw on the plugin-init argument, so every worker logs failed to load plugin (messages.filter / finish.includes / messages.map is not a function — whichever helper it reaches). The proxy still serves today only because OpenAIProxyPlugin happens to run first in Object.values order and Bun.serve fires as a side effect before any helper throws — i.e. it works by iteration-order luck.

With the descriptor present, readV1Plugin (packages/opencode/src/plugin/shared.ts) detects it and invokes only server.

Verification

Shipped-artifact path (not a wrapper): npm pack from this branch → installed the tarball into opencode's package cache → registered bare-name ("plugin": ["opencode-llm-proxy"]) in a scratch project → booted opencode serve (1.18.18, current latest) and forced instance creation:

• failed to load plugin lines: 0 (previously 1 per worker on every boot)
• proxy came up on its configured port; GET /v1/models → HTTP 200 with the model list

Unit suite: 232/232 pass (230 baseline + 2 new), eslint clean. New tests assert the descriptor shape and invoke descriptor.server({ client }) under the existing mocked-Bun fixture (hoisted to a shared withMockedBun helper) to prove the proxy actually boots through it.

Older-opencode behavior (no regression)

• readV1Plugin exists in every opencode release I checked back to v1.15.0, so the V1 path covers everything reasonably current.
• On loaders that predate it, the legacy path is still safe: getServerPlugin explicitly recognizes { server } objects (index.ts L88–93) — the descriptor is treated as a plugin whose server is OpenAIProxyPlugin, and the plugin's existing state.started guard makes the second invocation a no-op returning {}. Helper-probe log noise on those old builds is unchanged from today.

Extras

• .gitattributes with dist/** text eol=lf — the committed bundle is regenerated by prepack, so keeping it LF-only avoids whole-file churn on rebuilds.
• README gains a short Compatibility note (clean load on current opencode; harmless per-worker log line on very old builds) to pre-empt "still broken on 1.14" follow-ups.