Introduce "agents"

An agent is currently a name given to a system prompt and a set of
tools which the agent has access to.

This resolves the previous issue of the set of configured tools being
available in *all* contexts, which wasn't always desired. Tools are now
only available when an agent is explicitly requested using the
`-a/--agent` flag.

Agents are expected to be expanded on: the concept of task-specilized
agents (e.g. coding), the ability to define a set of files an agent
should always have access to for RAG purposes, etc.

Other changes:

- Removes the "tools" top-level config structure (though this is expected
to come back along with the abillity to define custom tools).

- Renamed `pkg/agent` to `pkg/agents`

pkg/agents/toolbox/read_file.go

@@ -0,0 +1,73 @@
+package toolbox
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	toolutil "git.mlow.ca/mlow/lmcli/pkg/agents/toolbox/util"
+	"git.mlow.ca/mlow/lmcli/pkg/api"
+)
+
+const READ_FILE_DESCRIPTION = `Retrieve the contents of a text file relative to the current working directory.
+
+Use the file contents for your own reference in completing your task, they do not need to be shown to the user.
+
+Each line of the returned content is prefixed with its line number and a tab (\t).
+
+Example result:
+{
+	"message": "success",
+	"result": "1\tthe contents\n2\tof the file\n"
+}`
+
+var ReadFileTool = api.ToolSpec{
+	Name:        "read_file",
+	Description: READ_FILE_DESCRIPTION,
+	Parameters: []api.ToolParameter{
+		{
+			Name:        "path",
+			Type:        "string",
+			Description: "Path to a file within the current working directory to read.",
+			Required:    true,
+		},
+	},
+
+	Impl: func(tool *api.ToolSpec, args map[string]interface{}) (string, error) {
+		tmp, ok := args["path"]
+		if !ok {
+			return "", fmt.Errorf("Path parameter to read_file was not included.")
+		}
+		path, ok := tmp.(string)
+		if !ok {
+			return "", fmt.Errorf("Invalid path in function arguments: %v", tmp)
+		}
+		result := readFile(path)
+		ret, err := result.ToJson()
+		if err != nil {
+			return "", fmt.Errorf("Could not serialize result: %v", err)
+		}
+		return ret, nil
+	},
+}
+
+func readFile(path string) api.CallResult {
+	ok, reason := toolutil.IsPathWithinCWD(path)
+	if !ok {
+		return api.CallResult{Message: reason}
+	}
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return api.CallResult{Message: fmt.Sprintf("Could not read path: %s", err.Error())}
+	}
+
+	lines := strings.Split(string(data), "\n")
+	content := strings.Builder{}
+	for i, line := range lines {
+		content.WriteString(fmt.Sprintf("%d\t%s\n", i+1, line))
+	}
+
+	return api.CallResult{
+		Result: content.String(),
+	}
+}