feat(FN-2718): add unavailable node policy setting and validation

- Define and export unavailable node policy types in core settings interfaces
- Add project-level unavailable node policy default and runtime validation helper
- Add core unit coverage for unavailable node policy parsing and acceptance cases
- Guard Paperclip mint requests to include companyId only when available for type-safe payloads
- Document unavailable node policy in the settings reference

packages/core/src/settings-schema.ts

@@ -77,6 +77,7 @@ export const DEFAULT_PROJECT_SETTINGS = {
   mergeStrategy: "direct",
   pushAfterMerge: false,
   pushRemote: "origin",
+  unavailableNodePolicy: "block",
   worktreeInitCommand: undefined,
   testCommand: undefined,
   buildCommand: undefined,