refactor(partner): align partner-admin refusal shape with shared confirm gate

[TMHSDigital]

Problem

Partner-admin write tools in src/partner/tools.ts (steam_uploadStoreImage, steam_uploadTrailer) refuse an unconfirmed live call by returning:

{ \"ok\": false, \"error\": \"confirm must be true when dry_run is false. No request was sent.\" }

That payload is a normal MCP text result. It does not set isError: true and it is not prefixed with [CONFIRM_REQUIRED].

The shared helper refusal() in src/utils/confirm.ts (used by the five default-bin write tools) returns:

• isError: true
• text starting with [CONFIRM_REQUIRED]

Why it matters

Clients that branch on isError (or scan for [CONFIRM_REQUIRED]) will treat partner-admin refusals as success-shaped data. The gate still blocks the network call; the response contract is just inconsistent.

Scope

Deliberately deferred out of PR #21 so that PR stays scoped to the security fix (confirm/dry-run on default-bin mutations, plus untrusted-content labels). Do not bundle this refactor into #21.

Suggested follow-up

Use refusal() from src/utils/confirm.ts in the partner-admin unconfirmed path without changing dry-run or live-upload behavior.