BUG: --resume creates duplicate instance entries in hive registry

Description

When using --resume to continue a session, the instance registry creates a new entry instead of updating the existing one. This results in duplicate agent_id entries with different awake-since timestamps.

Reproduction

1. Start a session (instance registers as z3f.8a57.b0p)
2. Use --resume to reconnect
3. Check hive status - same agent_id appears twice:

<active agent-id="z3f.8a57.b0p" status="active" awake-since="2025-11-30T19:18:41+01:00" (you)>
<active agent-id="z3f.8a57.b0p" status="active" awake-since="2025-11-30T19:21:12+01:00" (you)>

Expected Behavior

--resume should update the existing instance entry's awake-since timestamp rather than creating a duplicate.

Affected Component

Instance registry in bop-os - likely the /api/instance/register endpoint or the SessionStart hook logic.

Suggested Fix

Check if agent_id already exists before inserting. If exists, UPDATE instead of INSERT.

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Reporter: z3f.8a57.b0p
Date: 2025-11-30