Rename express/ to backend/ and update references

Update paths in sync.sh, master/main.go, and CLAUDE.md to reflect
the directory rename.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/diachron/auth/token.spec.ts

@@ -0,0 +1,94 @@
+// Tests for auth/token.ts
+// Pure unit tests - no database needed
+
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import {
+    generateToken,
+    hashToken,
+    parseAuthorizationHeader,
+    SESSION_COOKIE_NAME,
+} from "./token";
+
+describe("token", () => {
+    describe("generateToken", () => {
+        it("generates a non-empty string", () => {
+            const token = generateToken();
+            assert.equal(typeof token, "string");
+            assert.ok(token.length > 0);
+        });
+
+        it("generates unique tokens", () => {
+            const tokens = new Set<string>();
+            for (let i = 0; i < 100; i++) {
+                tokens.add(generateToken());
+            }
+            assert.equal(tokens.size, 100);
+        });
+
+        it("generates base64url encoded tokens", () => {
+            const token = generateToken();
+            // base64url uses A-Z, a-z, 0-9, -, _
+            assert.match(token, /^[A-Za-z0-9_-]+$/);
+        });
+    });
+
+    describe("hashToken", () => {
+        it("returns a hex string", () => {
+            const hash = hashToken("test-token");
+            assert.match(hash, /^[a-f0-9]+$/);
+        });
+
+        it("returns consistent hash for same input", () => {
+            const hash1 = hashToken("test-token");
+            const hash2 = hashToken("test-token");
+            assert.equal(hash1, hash2);
+        });
+
+        it("returns different hash for different input", () => {
+            const hash1 = hashToken("token-1");
+            const hash2 = hashToken("token-2");
+            assert.notEqual(hash1, hash2);
+        });
+
+        it("returns 64 character hash (SHA-256)", () => {
+            const hash = hashToken("test-token");
+            assert.equal(hash.length, 64);
+        });
+    });
+
+    describe("parseAuthorizationHeader", () => {
+        it("returns null for undefined header", () => {
+            assert.equal(parseAuthorizationHeader(undefined), null);
+        });
+
+        it("returns null for empty string", () => {
+            assert.equal(parseAuthorizationHeader(""), null);
+        });
+
+        it("returns null for non-bearer auth", () => {
+            assert.equal(parseAuthorizationHeader("Basic abc123"), null);
+        });
+
+        it("returns null for malformed header", () => {
+            assert.equal(parseAuthorizationHeader("Bearer"), null);
+            assert.equal(parseAuthorizationHeader("Bearer token extra"), null);
+        });
+
+        it("extracts token from valid bearer header", () => {
+            assert.equal(parseAuthorizationHeader("Bearer abc123"), "abc123");
+        });
+
+        it("is case-insensitive for Bearer keyword", () => {
+            assert.equal(parseAuthorizationHeader("bearer abc123"), "abc123");
+            assert.equal(parseAuthorizationHeader("BEARER abc123"), "abc123");
+        });
+    });
+
+    describe("SESSION_COOKIE_NAME", () => {
+        it("is defined", () => {
+            assert.equal(typeof SESSION_COOKIE_NAME, "string");
+            assert.ok(SESSION_COOKIE_NAME.length > 0);
+        });
+    });
+});