The terminal lists where you are signed in and ends one session with a confirm, as MCP `sessions` does #7237

For: someone who fears a lost laptop can sign it out from the terminal. Trust means seeing and ending your own sessions from any door.

accountSignIns and endAccountSession are reached from /settings (/settings/sessions/:id/delete) and MCP sessions. No terminal screen calls them.

Done:

• [ ] A new src/tui/screens/signins.ts, opened from the account palette as "Signed in". It lists your browsers and tokens, each with where, when it was last seen and its kind, and marks this one. It never shows a secret.
• [ ] d ends the selected session after a confirm. The current terminal session cannot be ended from here, and says so.
• [ ] A new test/tui-signins.test.ts covers: two sessions listed, end one after a confirm, then it is gone and its cookie reads as signed out. Another person's sessions are never listed.

Files: src/tui/screens/signins.ts, the palette's entry list, one test. Risk: low.