feat: support --effort flag via provider option and model suffix

[waveywaves]

Summary

• Adds an effort provider option (low | medium | high | xhigh | max) that forwards to claude --effort <level>.
• Also supports a per-model override using a modelId:effort suffix (e.g. opus:high), so one provider entry can expose multiple effort tiers without duplicating the whole block.

Why

Claude CLI's --effort controls reasoning depth, and there's currently no way to set it from opencode — the plugin only forwards --model and --dangerously-skip-permissions. This unblocks using e.g. opus at high effort alongside sonnet at default effort.

Usage

{
  "provider": {
    "claude-code": {
      "npm": "opencode-claude-code-plugin",
      "models": {
        "opus":     { "name": "Opus" },
        "opus:max": { "name": "Opus (max)" },
        "sonnet":   { "name": "Sonnet" }
      },
      "options": {
        "cliPath": "claude",
        "effort": "high"
      }
    }
  }
}

Resolution order:

1. If modelId has a :<effort> suffix and the suffix is valid, the suffix wins and is stripped before --model.
2. Otherwise fall back to options.effort.
3. If neither is set, --effort is omitted (current behavior).

Invalid suffixes are left untouched (treated as part of the model name) so existing configs keep working.

Test plan

• bun run typecheck
• bun run build
• Manual: DEBUG=opencode-claude-code opencode with effort: "high" set, verify --effort high appears in the spawned claude args.
• Manual: model keyed as opus:max, verify --model opus --effort max is spawned.