fix(books): downgrade archiver to v7 to restore zip export (#41)

archiver v8 switched to pure ESM with no default export and a
   completely different API, breaking every zip export request with
   TypeError: (0 , _archiver.default) is not a function. The NestJS
   SWC build produces CJS output, which cannot import the new ESM-only
   package at runtime.

   Downgrade to ~7.0.1 (the last CJS release) and add a Dependabot
   ignore rule for archiver major bumps so this cannot recur silently.

   Fixes #31

.github/dependabot.yml

@@ -14,6 +14,10 @@ updates:
       - "npm"
     commit-message:
       prefix: "chore(deps)"
+    ignore:
+      # archiver v8 is ESM-only with a completely different API; pin to v7 until we migrate
+      - dependency-name: "archiver"
+        update-types: ["version-update:semver-major"]
     groups:
       production-dependencies:
         dependency-type: "production"