feat: agent-to-agent platform on ZeroClaw 0.8.2 — rooms, delegation, A2A ingress

Builds on the v0.8.2 runtime. Four workstreams, all behind the §15 MCP door:

- Group rooms (Phase 1): migration 0026; N-way threads repo with a DM/room
  count-guard; chat.send {room} + room.create/invite/leave tools; RoomMessage
  -> room.message SSE; /api/claw-chat/rooms* APIs; Observer room badge.
- Per-claw door identity: door caller_agent resolves the X-ZeroClaw-Agent
  header (set by the fork) to the specific claw, falling back to roster[0].
- Gated delegation bridge (Phase 3): clawmates__delegate door tool drives a
  sibling via the existing /ws/chat ZeroClawDriveExecutor (not A2A); self-deny,
  per-workspace hourly budget, audit trail, untrusted-banner result. Native
  in-daemon delegation stays off (it would bypass the door).
- A2A tenant ingress (Phase 2): migration 0027 (workspace_a2a + a2a_tokens);
  runtime_provision enable_a2a_server/publish_claw; routes/a2a.rs tenant-aware
  proxy (per-workspace tokens, injected internal bearer, daemon stays internal,
  cards URL-rewritten to the cm-api edge); a2a.invoked taxonomy.

Tests: cm-db room repos, cm-runtime chat tools, door units. sqlx cache updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

.sqlx/query-a9941a9e8f56f22bcb779d19df4b714977577f9af49eac4ff63dcea0ed34167e.json

@@ -0,0 +1,16 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "INSERT INTO thread_participants (thread_id, agent_id, added_by) VALUES ($1, $2, $3)",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Uuid",
+        "Uuid",
+        "Uuid"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "a9941a9e8f56f22bcb779d19df4b714977577f9af49eac4ff63dcea0ed34167e"
+}