feat(approval): the approval seam — one-shot permission decisions over a waterfall of answerers

ctx.approval (dsh-approval): request() dispatches the approval/request
waterfall and always resolves a closed outcome — allowed-once / rejected /
cancelled / unavailable — never rejects; zero listeners fall through to
fail-closed unavailable; abort settles cancelled and discards late answers;
throwing or rogue answerers are contained as unavailable; every ask lands
the log-only approval/asked / approval/decided audit pair. dsh-tools routes
a pre-execute ask through the seam opportunistically (ctx.get) with three
distinct deny reasons, keeping the historical ask→deny degrade when the
seam is absent.

The per-session policy tier, the ACP bridge answerer, and the sandbox
escalation asker are staged follow-ups of the approval-seam RFC.

tsconfig.json

@@ -29,6 +29,7 @@
     { "path": "./packages/session-persistence/session-persistence-jsonl" },
     { "path": "./packages/session-persistence/session-persistence-sqlite" },
     { "path": "./packages/core/system-prompt" },
+    { "path": "./packages/approval/approval" },
     { "path": "./packages/core/agent" },
     { "path": "./packages/ui/user-interaction" },
     { "path": "./packages/core/tools" },