Project refactor, add anthropic API support

- Split pkg/cli/cmd.go into new pkg/cmd package
- Split pkg/cli/functions.go into pkg/lmcli/tools package
- Refactor pkg/cli/openai.go to pkg/lmcli/provider/openai

Other changes:

- Made models configurable
- Slight config reorganization

pkg/cmd/continue.go

@@ -0,0 +1,72 @@
+package cmd
+
+import (
+	"fmt"
+	"strings"
+
+	cmdutil "git.mlow.ca/mlow/lmcli/pkg/cmd/util"
+	"git.mlow.ca/mlow/lmcli/pkg/lmcli"
+	"git.mlow.ca/mlow/lmcli/pkg/lmcli/model"
+	"github.com/spf13/cobra"
+)
+
+func ContinueCmd(ctx *lmcli.Context) *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "continue <conversation>",
+		Short: "Continue a conversation from the last message",
+		Long:  `Re-prompt the conversation with all existing prompts. Useful if a reply was cut short.`,
+		Args: func(cmd *cobra.Command, args []string) error {
+			argCount := 1
+			if err := cobra.MinimumNArgs(argCount)(cmd, args); err != nil {
+				return err
+			}
+			return nil
+		},
+		RunE: func(cmd *cobra.Command, args []string) error {
+			shortName := args[0]
+			conversation := cmdutil.LookupConversation(ctx, shortName)
+
+			messages, err := ctx.Store.Messages(conversation)
+			if err != nil {
+				return fmt.Errorf("could not retrieve conversation messages: %v", err)
+			}
+
+			if len(messages) < 2 {
+				return fmt.Errorf("conversation expected to have at least 2 messages")
+			}
+
+			lastMessage := &messages[len(messages)-1]
+			if lastMessage.Role != model.MessageRoleAssistant {
+				return fmt.Errorf("the last message in the conversation is not an assistant message")
+			}
+
+			// Output the contents of the last message so far
+			fmt.Print(lastMessage.Content)
+
+			// Submit the LLM request, allowing it to continue the last message
+			continuedOutput, err := cmdutil.FetchAndShowCompletion(ctx, messages)
+			if err != nil {
+				return fmt.Errorf("error fetching LLM response: %v", err)
+			}
+
+			// Append the new response to the original message
+			lastMessage.Content += strings.TrimRight(continuedOutput[0].Content, "\n\t ")
+
+			// Update the original message
+			err = ctx.Store.UpdateMessage(lastMessage)
+			if err != nil {
+				return fmt.Errorf("could not update the last message: %v", err)
+			}
+
+			return nil
+		},
+		ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+			compMode := cobra.ShellCompDirectiveNoFileComp
+			if len(args) != 0 {
+				return nil, compMode
+			}
+			return ctx.Store.ConversationShortNameCompletions(toComplete), compMode
+		},
+	}
+	return cmd
+}