test(sf): advisor_allowed_providers dispatch gating

- Add behavioural tests for isProviderAllowedForAdvisor wired into
  selectAndApplyModel for subagent unit types.
- Verify non-subagent units are unaffected by the advisor allowlist.
- Add static source analysis guard confirming the check exists.

Assisted-by: Kimi Code CLI

src/resources/extensions/sf/tests/auto-model-selection.test.ts

@@ -660,7 +660,10 @@ test("selectAndApplyModel enforces advisor_allowed_providers for subagent units"
 				"advisor_allowed_providers:",
 				"  - anthropic",
 				"models:",
-				"  subagent: openai/gpt-4o",
+				"  subagent:",
+				"    model: openai/gpt-4o",
+				"    fallbacks:",
+				"      - anthropic/claude-sonnet-4-6",
 				"---",
 			].join("\n"),
 			"utf-8",