refactor(v2): move opencode provider off v2 trunk

v2 ships with only claude baked in. opencode now lives on the `providers`
branch and gets copied in via the /add-opencode skill.

Removed:
- src/providers/opencode.ts
- container/agent-runner/src/providers/{opencode,mcp-to-opencode}.ts + test
- @opencode-ai/sdk from agent-runner package.json + bun.lock
- opencode-ai global install + OPENCODE_VERSION ARG from Dockerfile
- opencode self-registration imports from both provider barrels
- opencode test case from factory.test.ts

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/providers/index.ts

@@ -5,4 +5,3 @@
 //
 // Skills add a new provider by appending one import line below.
 
-import './opencode.js';

src/providers/opencode.ts

@@ -1,49 +0,0 @@
-/**
- * Host-side container config for the `opencode` provider.
- *
- * OpenCode's `opencode serve` process stores state under XDG_DATA_HOME, which
- * we pin to a per-session host directory mounted at /opencode-xdg. The
- * OPENCODE_* env vars tell the CLI which provider/model to use at runtime
- * (read on the host, injected into the container). NO_PROXY / no_proxy are
- * merged with host values so the in-container OpenCode client can talk to
- * 127.0.0.1 even when HTTPS_PROXY is set by OneCLI.
- */
-import fs from 'fs';
-import path from 'path';
-
-import { registerProviderContainerConfig } from './provider-container-registry.js';
-
-function mergeNoProxy(current: string | undefined, additions: string): string {
-  if (!current?.trim()) return additions;
-  const parts = new Set(
-    current
-      .split(/[\s,]+/)
-      .map((s) => s.trim())
-      .filter(Boolean),
-  );
-  for (const addition of additions.split(',')) {
-    const trimmed = addition.trim();
-    if (trimmed) parts.add(trimmed);
-  }
-  return [...parts].join(',');
-}
-
-registerProviderContainerConfig('opencode', (ctx) => {
-  const opencodeDir = path.join(ctx.sessionDir, 'opencode-xdg');
-  fs.mkdirSync(opencodeDir, { recursive: true });
-
-  const env: Record<string, string> = {
-    XDG_DATA_HOME: '/opencode-xdg',
-    NO_PROXY: mergeNoProxy(ctx.hostEnv.NO_PROXY, '127.0.0.1,localhost'),
-    no_proxy: mergeNoProxy(ctx.hostEnv.no_proxy, '127.0.0.1,localhost'),
-  };
-  for (const key of ['OPENCODE_PROVIDER', 'OPENCODE_MODEL', 'OPENCODE_SMALL_MODEL'] as const) {
-    const value = ctx.hostEnv[key];
-    if (value) env[key] = value;
-  }
-
-  return {
-    mounts: [{ hostPath: opencodeDir, containerPath: '/opencode-xdg', readonly: false }],
-    env,
-  };
-});