herdr-core: restarting an agent in a terminal that was pinned before Ovis restarted unpins it in the Herdr app #2707

On herdr-core, Ovis keeps pinned agents in step with the Herdr app through herdr.pinned (#2694), remembering in herdr-core-pins.json what both sides last agreed on per terminal. A terminal that stopped running an agent while Ovis was stopped keeps its agreement, so a later restart of the agent there is read as an unpin made in Ovis.

Steps (OVIS_RUNTIME=herdr-core):

1. Pin an agent (e.g. Claude Code) in the Herdr app or in Ovis; both sides agree it is pinned.
2. Quit the agent in that terminal, leaving its shell, and restart the Ovis server (an update, say).
3. In Ovis, pin another agent: the Agents list drops the shell's pin, as it holds agents only.
4. Start the agent again in that terminal.

Expected: the Herdr app keeps it pinned.
Actual: Ovis writes herdr.pinned= (empty) and the Herdr app's pin is gone.

Cause: after a reconnect the bridge clears its set of agent terminals and reads the snapshot; a terminal that is no longer an agent never goes through the agent-to-shell transition, so its agreement is not dropped (server/herdr-core/pin-label.ts, agentIs). Reproduced by the review on fabe6f3 with the PR's fake hc.

Likely fix: while reading a snapshot, drop the agreement of every terminal whose status names no agent, and add a regression test for it.