stacks: add .env + .env.secrets.ctmpl for media stacks

Adds real Vault Agent secret templates and non-secret env vars for
all 15 media stacks. Sanitized real leaks found in the source data:
kodi's real username and real hostnames+IPs in KODI_INSTANCES,
tdarr's real IP and hostname reference, immich's real username -
replaced with generic values (IPs use the RFC 5737 documentation
range, 192.0.2.0/24, rather than another real-looking address).

Every var cross-checked against what its actual public compose file
references before writing, learned from the platform batch.

stacks/media/immich/.env.secrets.ctmpl

@@ -0,0 +1 @@
+DB_PASSWORD={{ with secret "kv/host/immich" }}{{ .Data.data.db_password }}{{ end }}