add ebooks stack: consolidate book services into single namespace [ci skip]

- New ebooks namespace with CWA, Stacks, Audiobookshelf, book-search
- book-search (renamed from audiobook-search) with CWA ingest volume
- Comment out audiobook_search module from servarr
- All NFS volumes and secrets consolidated

stacks/ebooks/tiers.tf

@@ -0,0 +1,10 @@
+# Generated by Terragrunt. Sig: nIlQXj57tbuaRZEa
+locals {
+  tiers = {
+    core    = "0-core"
+    cluster = "1-cluster"
+    gpu     = "2-gpu"
+    edge    = "3-edge"
+    aux     = "4-aux"
+  }
+}