fix(harnesses): migrate to ESO secrets_required form, mirror agent-runtimes

The CRS-served harnesses still carried `secrets_files: [{encrypted: true}]`
which now hard-fails on H-SECRET-1 ("SOPS-encrypted secrets_files entries
are no longer permitted") in the dispatcher's harness validator. Sync the
8 provider harnesses with the agent-runtimes copies: same `secrets_required`
shape, same `init.sh` (ESO-mounted file paths), same `bin/` wrappers.

Use bare `account_ref: "<provider>"` (not `<provider>.cp:cp` — that
scope-kind isn't valid per SR-DISP-1-FIELD).

Provider key names follow the per-provider schema as emitted by the CP
provisioner: minimax/airouter/z-ai → api_key; gitea-https/gitea-admin →
{token,base_url,username}; gitea-ssh* → {host,private_key}.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

harnesses/contexts/z-ai/v1/harness.yaml

@@ -11,9 +11,13 @@ env:
   CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC: "1"
   DISABLE_PROMPT_CACHING: "1"
 
-secrets_files:
-  - source: ./provider.sops.env
-    target: /opt/harness/secrets/z-ai/provider.sops.env
-    encrypted: true
+secrets_required:
+  - name: z-ai
+    account_ref: "z-ai"
+    mount_path: /run/agent/secrets/z-ai
+    mode: "0400"
+
+scripts:
+  init: "./init.sh"
 
 # TODO: Add network_hosts for api.z.ai when context harnesses support it