feat(v2): OpenCode agent provider

- Add OpenCodeProvider (SSE, session resume, MCP via mcp-to-opencode)
- Register opencode in factory; AGENT_PROVIDER passthrough from DB
- Host: XDG mount, NO_PROXY merge, OPENCODE_* env for opencode sessions
- Dockerfile: opencode-ai CLI; docs checklist + architecture diagram
- Skill add-opencode for v2; AgentProviderName in src/types.ts

Made-with: Cursor

container/Dockerfile

@@ -18,6 +18,7 @@ ARG INSTALL_CJK_FONTS=false
 ARG CLAUDE_CODE_VERSION=2.1.112
 ARG AGENT_BROWSER_VERSION=latest
 ARG VERCEL_VERSION=latest
+ARG OPENCODE_VERSION=latest
 ARG BUN_VERSION=1.3.12
 
 # ---- System dependencies -----------------------------------------------------
@@ -79,7 +80,8 @@ RUN --mount=type=cache,target=/root/.cache/pnpm \
     pnpm install -g \
         "@anthropic-ai/claude-code@${CLAUDE_CODE_VERSION}" \
         "agent-browser@${AGENT_BROWSER_VERSION}" \
-        "vercel@${VERCEL_VERSION}"
+        "vercel@${VERCEL_VERSION}" \
+        "opencode-ai@${OPENCODE_VERSION}"
 
 # ---- agent-runner ------------------------------------------------------------
 WORKDIR /app