feat: add Honcho memory provider with PostgreSQL + pgvector stack

Add Honcho (https://github.com/plastic-labs/honcho) as a self-hosted
memory infrastructure for stateful AI agents.

Changes:
- ai/honcho/Dockerfile: multi-stage build from Honcho GitHub source
- ai/honcho/init.sql: CREATE EXTENSION vector for pgvector
- ai/compose.yml: add honcho-db (pgvector/pgvector:pg17-trixie) and
  honcho services with ai_backend/ai_net networking and Traefik labels
- build/honcho/config.toml: pre-configured for Ollama embeddings
  (nomic-embed-text via http://ollama:11434/v1), deriver/summary/dream
  disabled by default
- env/.env.example.honcho: sample env vars (HONCHO_DB_PASSWORD,
  LLM_OPENAI_API_KEY)

Usage:
  cp env/.env.example.honcho .env  # edit secrets
  mkdir -p /mnt/HoardingCow_docker_data/Honcho
  cp build/honcho/config.toml /mnt/HoardingCow_docker_data/Honcho/config.toml
  docker compose -f ai/compose.yml up honcho

env/.env.example.honcho

@@ -0,0 +1,31 @@
+# Honcho Environment Variables
+# Copy this file to your .env (at the compose root or docker-compose working directory)
+# and fill in the secrets.
+#
+#   cp env/.env.example.honcho .env
+#
+# Then reference it from compose.yml:
+#   env_file:
+#     - path: .env
+#       required: true
+
+# ---------------------------------------------------------------------------
+# Database
+# ---------------------------------------------------------------------------
+# PostgreSQL connection string for Honcho.
+# The password must match HONCHO_DB_PASSWORD below.
+HONCHO_DB_PASSWORD=change_me_to_a_strong_random_password
+
+# ---------------------------------------------------------------------------
+# LLM Provider
+# ---------------------------------------------------------------------------
+# Ollama does not require a real API key, but the env var must be set to a
+# non-empty string for the OpenAI-compatible client to connect.
+LLM_OPENAI_API_KEY=ollama
+
+# ---------------------------------------------------------------------------
+# Honcho Server
+# ---------------------------------------------------------------------------
+# Honcho will pick up DB_CONNECTION_URI from the compose environment.
+# You can override additional settings here if needed.
+# LOG_LEVEL=INFO