fix(hooks): use API instead of filesystem to resolve model info for session.prompt

Previously, continuation hooks (todo-continuation, boulder-continuation, ralph-loop)
and background tasks resolved model info from filesystem cache, which could be stale
or missing. This caused session.prompt to fallback to default model (Sonnet) instead
of using the originally configured model (e.g., Opus).

Now all session.prompt calls first try API (session.messages) to get current model
info, with filesystem as fallback if API fails.

Affected files:
- todo-continuation-enforcer.ts
- sisyphus-orchestrator/index.ts
- ralph-loop/index.ts
- background-agent/manager.ts
- sisyphus-task/tools.ts
- hook-message-injector/index.ts (export ToolPermission type)

src/features/hook-message-injector/index.ts

@@ -1,4 +1,4 @@
 export { injectHookMessage, findNearestMessageWithFields, findFirstMessageWithAgent } from "./injector"
 export type { StoredMessage } from "./injector"
-export type { MessageMeta, OriginalMessageContext, TextPart } from "./types"
+export type { MessageMeta, OriginalMessageContext, TextPart, ToolPermission } from "./types"
 export { MESSAGE_STORAGE } from "./constants"