Unblock daily workflow startup failures in doc-healer (Claude model) and model-inventory (Copilot SDK auth)

[Copilot]

Two scheduled workflows were failing before first agent turn due to startup config regressions: Documentation Healer hit an unsupported Claude effort path, and Model Inventory Checker lost token auth in Copilot SDK driver execution. This PR removes the failing model path in doc-healer and restores runtime auth token availability for copilot-sdk agent startup.

• Documentation Healer: remove unsupported small-agent execution path

  • Pin .github/workflows/daily-doc-healer.md to engine.model: "agent".
  • Remove the model_size experiment block that introduced small-agent.
  • Recompile lockfile to remove experiment wiring and ensure the runtime model resolves to agent.

• Model Inventory Checker: restore auth token plumbing for Copilot SDK agent runs

  • In pkg/workflow/copilot_engine_execution.go, stop emitting --exclude-env COPILOT_GITHUB_TOKEN when engine.copilot-sdk: true.
  • Keep existing BYOK behavior unchanged; this adjustment is specific to copilot-sdk mode where the driver must access auth in-process to create the session.
  • Recompile daily-model-inventory.lock.yml so the generated AWF command reflects the new exclusion behavior.

• Regression guard

  • Add a focused test in pkg/workflow/copilot_engine_test.go asserting copilot-sdk mode does not exclude COPILOT_GITHUB_TOKEN.

// copilot-sdk mode must keep COPILOT_GITHUB_TOKEN visible to the driver runtime.
if !isBYOKMode && !isCopilotSDKMode {
	copilotCoreSecrets = []string{"COPILOT_GITHUB_TOKEN"}
}