feat: add amcs-cli — MCP tool CLI and stdio bridge

- cmd/amcs-cli: new CLI tool for human/AI MCP tool access
- amcs-cli tools: list all tools from remote MCP server
- amcs-cli call <tool> --arg k=v: invoke a tool, print JSON/YAML result
- amcs-cli stdio: stdio→HTTP MCP bridge for AI clients
- Config: ~/.config/amcs/config.yaml, AMCS_URL/AMCS_TOKEN env vars, --server/--token flags
- Token never logged in errors
- Makefile: add build-cli target

Closes #18

cmd/amcs-cli/main.go

@@ -0,0 +1,7 @@
+package main
+
+import "git.warky.dev/wdevs/amcs/cmd/amcs-cli/cmd"
+
+func main() {
+	cmd.Execute()
+}