Adaptive review

[LinceMathew]

Summary

Provisions Adaptive Review support during git-lrc setup by creating a second, cheaper "helper" AI connector alongside the existing "leader" connector.

Today, git-lrc setup only creates one Gemini connector (gemini-2.5-flash). Adaptive Review on the LiveReview backend uses a leader/helper model pair — a strong model for full reviews and a lightweight model for cheaper/faster passes. This PR makes setup provision both automatically:

• Adds a Role field ("leader" / "helper") to CreateConnectorRequest and ConnectorRemote, threaded through connector creation, config rendering, and the API response.
• After the existing leader connector is created, setup now also creates a Gemini Flash-Lite helper connector (gemini-2.5-flash-lite), reusing the same free Gemini key — no second key prompt required.
• Helper connector creation is best-effort: if it fails, setup does not fail overall. The org falls back to leader-only and can configure a helper connector later; a warning is printed and logged.
• config/ai_connectors.go now writes role = "..." into the rendered TOML for every connector, defaulting empty/legacy roles to "leader" for backward compatibility with older configs.
• Refactored setup/connectors.go to remove duplication between CreateGeminiConnector and CreateGeminiHelperConnector: extracted a shared createConnector() helper (network call, status check, error handling) and a defaultAPIURL() helper reused by ValidateGeminiKey too.

Linked Issue

Add the issue link this PR fulfills.

Validation

• go build ./... — passes.
• go test ./setup/... ./internal/appui/... ./config/... — passes.
• New/updated unit tests:
  • setup/connectors_test.go: helper connector sends role="helper" + lite model + reused key; leader connector sends role="leader" + default model.
  • internal/appui/ui_connectors_test.go: config rendering writes role = "leader" for explicit-leader and empty-role (legacy) connectors, and role = "helper" for helper connectors.

Checklist

• This PR fulfills an agreed issue.
• I kept the change narrow and scoped.
• I ran the most specific relevant validation and described it above.
• If I changed behavior, I called that out clearly in this PR.
• If I touched UI, I attached a GIF or video walkthrough. This is required. (N/A — CLI setup output only, no UI)
• If I changed storage/ responsibilities, I updated storage/storage_status.md and ran make check-status-doc. (N/A — no storage/ changes)
• If I changed network/ responsibilities, I updated network/network_status.md and ran make check-status-doc. (N/A — network/ package itself untouched; only callers changed)
• If this change touches security, disclosure flow, credentials, storage, network behavior, or remote data handling, I reviewed SECURITY.md and updated related documentation if needed. (Reuses the existing validated Gemini key for a second connector — no new credential handling introduced; please confirm this doesn't need a SECURITY.md note.)