feat: add container support with Containerfile and make targets

- Containerfile: python:3.13-slim base, pip install, copy plugins
- .containerignore: exclude dev artifacts from build context
- Makefile: add build, container-run, container-stop, container-logs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Makefile

@@ -1,5 +1,6 @@
-.PHONY: install dev test lint clean help
+.PHONY: install dev test lint clean help build container-run container-stop container-logs
 
+APP_NAME := derp
 VENV := .venv
 PIP := $(VENV)/bin/pip
 PYTHON := $(VENV)/bin/python
@@ -37,3 +38,17 @@ clean: ## Remove build artifacts
 link: install ## Symlink to ~/.local/bin
 	ln -sf $$(pwd)/$(VENV)/bin/derp ~/.local/bin/derp
 	@echo "Installed: $$(which derp)"
+
+build: ## Build container image
+	podman build -t $(APP_NAME) .
+
+container-run: ## Run bot in container (mount config)
+	podman run -d --name $(APP_NAME) \
+		-v ./config/derp.toml:/app/config/derp.toml:ro,Z \
+		$(APP_NAME)
+
+container-stop: ## Stop and remove container
+	podman stop $(APP_NAME) && podman rm $(APP_NAME)
+
+container-logs: ## Follow container logs
+	podman logs -f $(APP_NAME)