feat(installer): add --opencode target

[steventohme]

Summary

Adds opencode (https://opencode.ai) as a third install target alongside Claude Code and Codex. One command — npx @workweave/router --opencode — and opencode routes through the Weave Router. No router-side change needed; the router speaks Anthropic Messages natively, so opencode's bundled @ai-sdk/anthropic provider talks to it unmodified.

What's in the diff

• install/install.sh — new --opencode flag, picker entry (option 3), per-target scope path resolution, and a write_opencode_config() helper that jq-merges a managed provider.weave block into opencode.json. Dispatch block parallels the existing --codex branch (health ping, key validation, gitignore for project scope, OPENCODE_CONFIG= hint for --dir installs).
• install/uninstall.sh — --opencode strip path. Structurally removes provider.weave and the top-level model only when it points at weave/...; deletes the file if nothing non-schema remains.
• READMEs — root README.md, install/README.md, and install/npm/README.md updated with the new flag, scope paths, and onboarding flow.

Config layout

Scope	Path
user	~/.config/opencode/opencode.json (honors $XDG_CONFIG_HOME)
project	<repo>/opencode.json (gitignored, per-teammate key)
--dir <d>	<d>/opencode.json (caller sets OPENCODE_CONFIG)

Managed block:

"provider": {
  "weave": {
    "npm": "@ai-sdk/anthropic",
    "name": "Weave Router",
    "options": {
      "baseURL": "https://router.workweave.ai/v1",
      "headers": {
        "X-Weave-Router-Key": "rk_...",
        "X-App": "opencode",
        "X-Weave-User-Email": "...",
        "X-Weave-User-Name": "..."
      }
    },
    "models": { "claude-opus-4-7": {...}, "claude-sonnet-4-6": {...}, "claude-haiku-4-5": {...} }
  }
}

Top-level model is set to weave/claude-sonnet-4-6 only when the user hasn't already chosen one. Other providers, MCP servers, agents, and unrelated keys are preserved across re-install / uninstall.

Test plan

• bash -n install/install.sh and bash -n install/uninstall.sh clean
• Fresh install (--opencode --dir <tmp> --non-interactive) — file 0600, well-formed, identity headers landed
• Idempotent re-install over an opencode.json that already has a user-chosen model and an unrelated provider.openai — both preserved, weave merged alongside
• Full roundtrip: install → uninstall preserves user data
• Uninstall on a clean-install file deletes it (no zero-key artifact)
• Live test with the opencode CLI installed (smoke tests ran without opencode on PATH; CLI presence is a warning, not a hard fail)

Follow-ups (not in this PR)

• WorkWeave-side gitlink bump + syncrouterinstall/install_template.sh mirror sync once this merges
• Bump @workweave/router npm package version after merge

🤖 Generated with Claude Code