feat(permissions): unknown-sender request_approval flow + flipped default policy

When an unknown sender writes into a wired messaging group, surface the
situation to an admin instead of silently dropping. Flow:

  1. Router → access gate → handleUnknownSender (policy='request_approval')
  2. Fire-and-forget requestSenderApproval: pickApprover + pickApprovalDelivery
     pick a reachable admin DM; deliver an Approve / Deny card; insert a
     pending_sender_approvals row carrying the original InboundEvent JSON.
  3. In-flight dedup: UNIQUE(messaging_group_id, sender_identity) — a retry
     from the same stranger while pending is silently dropped, not re-carded.
  4. Admin clicks → Chat SDK bridge → onAction → host response-registry.
     The new handleSenderApprovalResponse in the permissions module claims
     responses whose questionId matches a pending_sender_approvals row.
  5. approve: addMember(stranger, agent_group) + replay the stored event via
     routeInbound — the second attempt clears the gate because the user is
     now known.
  6. deny: delete the pending row. No denial persistence (ACTION-ITEMS item 5
     decision) — a future attempt triggers a fresh card.

Schema:
- Migration 011 adds pending_sender_approvals (id, mg_id, agent_group_id,
  sender_identity, sender_name, original_message JSON, approver_user_id,
  created_at, UNIQUE(mg_id, sender_identity)).
- Also flips messaging_groups.unknown_sender_policy default from 'strict'
  to 'request_approval' (rebuild-table). Existing rows unchanged — only
  the default applied to new rows flips.
- Router auto-create for unknown platform/chat drops the hardcoded
  'strict' override; schema default applies.
- src/db/schema.ts reference updated to match.

Why default-flip: users wire their DM during setup and don't discover that
'strict' means "silent drop of everyone not in user_roles/members". The
approval flow is the safe default — the admin sees the stranger, explicitly
decides. 'public' stays opt-in for truly open channels.

Failure modes (row NOT created so a future attempt can try again):
- No eligible approver configured (fresh install before first owner).
- No reachable DM for any approver.
- Delivery adapter missing.

Tests (src/modules/permissions/sender-approval.test.ts, 4 cases):
- First unknown message → card delivered + row created
- Retry while pending → dedup'd (1 card, 1 row)
- Approve → member added + message replayed + container woken
- Deny → row cleared + no member added

Closes: ACTION-ITEMS item 5.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/modules/permissions/db/pending-sender-approvals.ts

@@ -0,0 +1,59 @@
+/**
+ * CRUD for pending_sender_approvals — the in-flight state for the
+ * request_approval unknown-sender flow. Rows are created when an unknown
+ * sender writes into a wired messaging group with that policy, and are
+ * deleted on admin approve (after adding the user as a member) or deny.
+ *
+ * UNIQUE(messaging_group_id, sender_identity) enforces in-flight dedup:
+ * a retry / second message from the same unknown sender while a card is
+ * still pending is silently dropped instead of spamming the admin.
+ */
+import { getDb } from '../../../db/connection.js';
+
+export interface PendingSenderApproval {
+  id: string;
+  messaging_group_id: string;
+  agent_group_id: string;
+  sender_identity: string;
+  sender_name: string | null;
+  original_message: string;
+  approver_user_id: string;
+  created_at: string;
+}
+
+export function createPendingSenderApproval(row: PendingSenderApproval): void {
+  getDb()
+    .prepare(
+      `INSERT INTO pending_sender_approvals (
+         id, messaging_group_id, agent_group_id, sender_identity,
+         sender_name, original_message, approver_user_id, created_at
+       )
+       VALUES (
+         @id, @messaging_group_id, @agent_group_id, @sender_identity,
+         @sender_name, @original_message, @approver_user_id, @created_at
+       )`,
+    )
+    .run(row);
+}
+
+export function getPendingSenderApproval(id: string): PendingSenderApproval | undefined {
+  return getDb()
+    .prepare('SELECT * FROM pending_sender_approvals WHERE id = ?')
+    .get(id) as PendingSenderApproval | undefined;
+}
+
+export function hasInFlightSenderApproval(
+  messagingGroupId: string,
+  senderIdentity: string,
+): boolean {
+  const row = getDb()
+    .prepare(
+      'SELECT 1 AS x FROM pending_sender_approvals WHERE messaging_group_id = ? AND sender_identity = ?',
+    )
+    .get(messagingGroupId, senderIdentity) as { x: number } | undefined;
+  return row !== undefined;
+}
+
+export function deletePendingSenderApproval(id: string): void {
+  getDb().prepare('DELETE FROM pending_sender_approvals WHERE id = ?').run(id);
+}