mention: book the seats' spend to the ledger as the time bot

The mention runner's ledger flush was failing on every reply ("User permission denied for
writing"): main is PR-only for the Actions identity, and this workflow was the only one not
handed TIME_TOKEN, so @seat replies went unbooked and the daily governor undercounted them.
Same env line the heartbeat, venture and astra workflows already carry.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LaVWDr6h62YJk9LJqvQH7k

.github/workflows/mention.yml

@@ -32,6 +32,7 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           VENICE_API_KEY: ${{ secrets.VENICE_API_KEY }}
           ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
+          TIME_TOKEN: ${{ secrets.TIME_TOKEN }}   # repo secret: the ledger flush pushes to main as the `time` bot (the Actions identity may not)
           TIME_TRUSTED: ${{ vars.TIME_TRUSTED }}   # org owners etc.; collaborators are trusted without being listed
           TIME_DAILY_USD: ${{ vars.TIME_DAILY_USD }}
           TIME_MONTHLY_USD: ${{ vars.TIME_MONTHLY_USD }}