Add database migrations

db/migrations/0002-optimise-profile-content.up.js

@@ -0,0 +1,13 @@
+module.exports = async function(db) {
+	const hasher = await require("xxhash-wasm")()
+	const contents = db.prepare("SELECT distinct hashed_profile_content FROM sim_member WHERE hashed_profile_content IS NOT NULL").pluck().all()
+	const stmt = db.prepare("UPDATE sim_member SET hashed_profile_content = ? WHERE hashed_profile_content = ?")
+	db.transaction(() => {
+		for (let s of contents) {
+			let b = Buffer.isBuffer(s) ? Uint8Array.from(s) : Uint8Array.from(Buffer.from(s))
+			const unsignedHash = hasher.h64Raw(b)
+			const signedHash = unsignedHash - 0x8000000000000000n // shifting down to signed 64-bit range
+			stmt.run(signedHash, s)
+		}
+	})()
+}