[ci skip] Move Terraform modules into stack directories

Move all 88 service modules (66 individual + 22 platform) from
modules/kubernetes/<service>/ into their corresponding stack directories:

- Service stacks: stacks/<service>/module/
- Platform stack: stacks/platform/modules/<service>/

This collocates module source code with its Terragrunt definition.
Only shared utility modules remain in modules/kubernetes/:
ingress_factory, setup_tls_secret, dockerhub_secret, oauth-proxy.

All cross-references to shared modules updated to use correct
relative paths. Verified with terragrunt run --all -- plan:
0 adds, 0 destroys across all 68 stacks.

stacks/platform/modules/wireguard/extra/clients.conf

@@ -0,0 +1,4 @@
+[Peer]
+# friendly_name = anca
+PublicKey = fr4DB6FHhxYyzrtnoNbhdT8Fqwvsz7QkhTnZpSQmBCY=
+AllowedIPs = 10.3.3.13/32

stacks/platform/modules/wireguard/extra/last_ip.txt

@@ -0,0 +1 @@
+# DO NOT MANUALLY EDIT THIS LINE. Last IP: 10.3.3.15/24