feat(opencode): cut plugin system and remote behavior feeds; add SessionContext assembly and Runner

- delete plugin machinery (loader, install, meta, hooks) and all trigger sites
- fold first-party provider auth into static registry (provider/hooks.ts)
- remove remote instruction URL fetch, skills remote puller, TUI plugin host
- add session/context.ts: single provenance-tagged context assembly point
- add session/runner.ts: admit/context/stream/tools loop with compaction policy
- relocate audit artifacts to audit/ (FORK-AUDIT, instruction docs as evidence)

packages/opencode/test/provider/header-timeout.test.ts

@@ -10,7 +10,6 @@ import { disposeAllInstances, provideTmpdirInstance } from "../fixture/fixture"
 import { testEffect } from "../lib/effect"
 import { testProviderConfig } from "../lib/test-provider"
 import { Env } from "@/env"
-import { Plugin } from "@/plugin"
 import { Provider } from "@/provider/provider"
 import { ProviderError } from "@/provider/error"
 
@@ -19,7 +18,7 @@ afterEach(async () => {
 })
 
 const it = testEffect(
-  LayerNode.compile(LayerNode.group([Provider.node, Env.node, Plugin.node, CrossSpawnSpawner.node])),
+  LayerNode.compile(LayerNode.group([Provider.node, Env.node, CrossSpawnSpawner.node])),
 )
 
 it.live("headerTimeout does not abort delayed SSE body after headers arrive", () =>