feat(taski): send internal auth to exesh

[DIvanCode]

Closes#323

Taski now reads InternalAuthKey and sends it to Exesh both when creating an execution and when polling its message history. Local and end-to-end configurations use INTERNAL_AUTH_KEY_LOCAL_VALUE; the deployment playbook reads internal_auth_key from encrypted credentials and validates it before deployment work begins. The execution and REST polling process documentation reflects the authenticated requests.

Operator action before Ready for review: add the same non-local internal_auth_key to the encrypted credentials used by Duely, Taski, Exesh, and later Analyzer. Do not commit the plaintext value.

Validation:

• go test ./...
• ./e2e/taski-exesh/run.sh — accepted A+B solution
• ansible-playbook --syntax-check with temporary non-secret test variables