Switch to directory mount for opencode config, update docs with make

Mount ~/.config/opencode as a directory instead of individual files.
This persists all config changes (opencode.json, oh-my-opencode-slim.json,
skills) across container restarts. Add make to README architecture diagram.

docker-compose.yml

@@ -31,16 +31,14 @@ services:
       # SSH keys (read-only) — for git push/pull
       - ${SSH_KEY_PATH:-~/.ssh}:/home/developer/.ssh:ro
 
-      # Optional: mount your own opencode config (MCP servers, custom models, etc.)
-      # - ./opencode.json:/home/developer/.config/opencode/opencode.json:ro
+      # Optional: mount opencode config directory (persists config changes across restarts)
+      # Includes opencode.json, oh-my-opencode-slim.json, skills, etc.
+      # When mounted, OPENCODE_PROVIDER auto-config is skipped if opencode.json exists.
+      # - ~/.config/opencode:/home/developer/.config/opencode
 
-      # Optional: mount opencode skills from host
-      # - ~/.config/opencode/skills:/home/developer/.config/opencode/skills:ro
+      # Optional: mount opencode agent skills from host
       # - ~/.agents/skills:/home/developer/.agents/skills:ro
 
-      # Optional: mount your own oh-my-opencode-slim config
-      # - ./oh-my-opencode-slim.json:/home/developer/.config/opencode/oh-my-opencode-slim.json:ro
-
       # Optional: mount neovim config from host (plugins auto-install on first start)
       # - ~/.config/nvim:/home/developer/.config/nvim:ro