Set AUTH_HMAC_SECRET default to "io.github.pnoker.dc3" across .env
templates, compose files, and Java config properties so that X-Auth-User
header signing is active out of the box without manual configuration.
Expose AGENTIC_MEMORY_ENABLED, AGENTIC_TOOL_CALLING_ENABLED,
AGENTIC_MEMORY_MAX_MESSAGES, and AGENTIC_ATTACHMENT_STORAGE_PATH
in development and production compose files, with defaults in dev.env.
Also mark OpenAI base-url config as deprecated in application-agentic.yml.
The HMAC signing feature was dormant because no deployment config
set the shared secret. Add AUTH_HMAC_SECRET to .env.example, dev
env files, both compose stacks (all 12 services), and document it
in ENVIRONMENT.md.