Allow launchers to skip initial Claude setModel

[imwalkinhere]

Summary

• add a launcher-controlled escape hatch for the initial query.setModel(...) call when the model is already baked into the Claude subprocess environment
• treat both CLAUDE_AGENT_ACP_SKIP_INITIAL_SET_MODEL=1 and the existing OpenClaw-facing CLAUDE_ACP_BAKE_MODEL=1 marker as signals to skip the redundant setModel call
• cover the behavior with a settings test that selects the current model from ANTHROPIC_MODEL without calling setModel

Context

Some ACP launchers select the Claude model before process startup via environment variables. In that mode, immediately replaying setModel after initialization can hit provider/runtime paths that are more fragile than launch-time model selection. This keeps the default behavior unchanged unless a launcher explicitly opts into the skip marker.

Tests

• npm run test:run -- src/tests/acp-agent-settings.test.ts
• npm run build
• npm run format:check
• npm run lint