address-findings: fix branch-selector gap and auth message

Address Cursor Bugbot review findings on PR #32:

• Branch input never mapped to a trail number: the skill told agents to pass a bare branch through unchanged but then used <number> everywhere. Since entire trail accepts a number, id, or branch interchangeably as the selector, switch the workflow to a single <trail> selector (and match by number OR branch in the branch guard) instead of requiring a number lookup.
• Auth message omitted the gated command: name entire trail finding list in both the step 3 and failure-mode auth messages, matching peer skills.