Add member identifiers table for ID documents (DL, passport, school ID)

member_identifier table with type, value, issuing authority, expiry,
front/back image storage (base64 in Postgres), primary flag. CRUD
endpoints under /members/:memberId/identifiers. Zod schemas with
constrained type enum.

packages/backend/src/db/migrations/meta/_journal.json

@@ -71,6 +71,13 @@
       "when": 1774703400000,
       "tag": "0009_member_number",
       "breakpoints": true
+    },
+    {
+      "idx": 10,
+      "version": "7",
+      "when": 1774704000000,
+      "tag": "0010_member_identifiers",
+      "breakpoints": true
     }
   ]
 }