Project groups — link dirs to share runs / chats / memory

A GROUP links several project directories so their runs, chats, and long-term memory collaborate across projects (one Cyberine group = one shared memory pool). Groups are OPT-IN: with no config, every directory stays isolated exactly as before.

Define groups in <CYBERINE_HOME>/groups.json (honors CYBERINE_HOME):

{
  "groups": [
    {
      "id": "acme",
      "workspace": "acme-ws",
      "cwds": ["/Users/me/work/acme-api"],
      "pathPrefixes": ["/Users/me/work/acme"]
    }
  ]
}

A cwd joins a group by an EXACT cwds match (wins) or by falling under a pathPrefixes entry (longest prefix wins). workspace defaults to the group id.

cyberine group which          # which group the current directory is in (or "not in any group")
cyberine group list           # all configured groups + their workspace + path count
cyberine group runs [id]      # runs across the group's dirs (defaults to this dir's group; or pass an id)
cyberine group chats [id]     # chat sessions across the group's dirs

The core effect: when a run's cwd is in a group, buildMemoryPreamble reads the COMBINED memory of all the group's dirs — so a run in acme-api sees the handoffs/lessons/facts recorded in any sibling dir of the acme group. GUARDRAIL: only explicitly-configured dirs are grouped; never group unrelated clients (their memory would cross-contaminate).