feat: tool approval declarations (v9)

Agent definitions gain tool_approvals: known tool -> ask/auto/deny.
Unknown tool/policy is a 400, and required+deny is a 400
contradiction. The declaration is persisted (tasks.agent_tool_
approvals, PG + migrate), echoed in GET and the creation response
(via to_summary), and resolved for registry definitions -- fixing
a latent drop where resolve_registry_agent re-parsed without new
fields. At dispatch the worker audits the declaration and fails
fast on a defensive required+deny re-check (v3 tools-gate shape,
runner never called); goal/coordinator tasks reject the field at
creation like instructions. effective_tool_approvals maps a
declaration + host global approval to the actual host answer,
with ask_honoured always False: host answers elicitation with
one global switch and carries no tool identity, and the approvals
queue is record-only with no runtime ask channel, so per-tool
interception and credential scope are explicitly NOT claimed.

cloud/db.py

@@ -896,6 +896,7 @@ POSTGRES_SCHEMA = (
     "agent_version TEXT, "
     "agent_instructions TEXT, "
     "agent_tools TEXT, "
+    "agent_tool_approvals TEXT, "
     "UNIQUE(project_id, idempotency_key))",
     "CREATE INDEX IF NOT EXISTS idx_tasks_status ON tasks(status)",
     # 附件包与任务附件：与 server._ensure_uploads_tables 同款，