Add agent config revisions, issue-approval links, and robust migration reconciliation

Add agent_config_revisions table for tracking agent configuration changes with
rollback support. Add issue_approvals junction table linking issues to approvals.
New migrations (0005, 0006) for permissions column and new tables. Rework migration
client with statement-level idempotency checks (table/column/index/constraint
existence) so migrations can be safely retried against partially-migrated databases.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/db/src/schema/issue_approvals.ts

@@ -0,0 +1,23 @@
+import { pgTable, uuid, text, timestamp, index, primaryKey } from "drizzle-orm/pg-core";
+import { companies } from "./companies.js";
+import { issues } from "./issues.js";
+import { approvals } from "./approvals.js";
+import { agents } from "./agents.js";
+
+export const issueApprovals = pgTable(
+  "issue_approvals",
+  {
+    companyId: uuid("company_id").notNull().references(() => companies.id),
+    issueId: uuid("issue_id").notNull().references(() => issues.id, { onDelete: "cascade" }),
+    approvalId: uuid("approval_id").notNull().references(() => approvals.id, { onDelete: "cascade" }),
+    linkedByAgentId: uuid("linked_by_agent_id").references(() => agents.id, { onDelete: "set null" }),
+    linkedByUserId: text("linked_by_user_id"),
+    createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
+  },
+  (table) => ({
+    pk: primaryKey({ columns: [table.issueId, table.approvalId], name: "issue_approvals_pk" }),
+    issueIdx: index("issue_approvals_issue_idx").on(table.issueId),
+    approvalIdx: index("issue_approvals_approval_idx").on(table.approvalId),
+    companyIdx: index("issue_approvals_company_idx").on(table.companyId),
+  }),
+);