Large refactor - it compiles!

This refactor splits out all conversation concerns into a new
`conversation` package. There is now a split between `conversation` and
`api`s representation of `Message`, the latter storing the minimum
information required for interaction with LLM providers. There is
necessary conversation between the two when making LLM calls.

pkg/conversation/conversation.go

@@ -0,0 +1,98 @@
+package conversation
+
+import (
+	"database/sql"
+	"database/sql/driver"
+	"encoding/json"
+	"fmt"
+	"time"
+
+	"git.mlow.ca/mlow/lmcli/pkg/api"
+)
+
+type Conversation struct {
+	ID             uint `gorm:"primaryKey"`
+	ShortName      sql.NullString
+	Title          string
+	SelectedRootID *uint
+	SelectedRoot   *Message  `gorm:"foreignKey:SelectedRootID"`
+	RootMessages   []Message `gorm:"-:all"`
+}
+
+type MessageMeta struct {
+	GenerationProvider *string `json:"generation_provider,omitempty"`
+	GenerationModel    *string `json:"generation_model,omitempty"`
+}
+
+type Message struct {
+	ID        uint `gorm:"primaryKey"`
+	CreatedAt time.Time
+	Metadata  MessageMeta
+
+	ConversationID  *uint         `gorm:"index"`
+	Conversation    *Conversation `gorm:"foreignKey:ConversationID"`
+	ParentID        *uint
+	Parent          *Message  `gorm:"foreignKey:ParentID"`
+	Replies         []Message `gorm:"foreignKey:ParentID"`
+	SelectedReplyID *uint
+	SelectedReply   *Message `gorm:"foreignKey:SelectedReplyID"`
+
+	Role        api.MessageRole
+	Content     string
+	ToolCalls   ToolCalls   // a json array of tool calls (from the model)
+	ToolResults ToolResults // a json array of tool results
+}
+
+func (m *MessageMeta) Scan(value interface{}) error {
+	return json.Unmarshal(value.([]byte), m)
+}
+
+func (m MessageMeta) Value() (driver.Value, error) {
+	return json.Marshal(m)
+}
+
+type ToolCalls []api.ToolCall
+
+func (tc *ToolCalls) Scan(value any) (err error) {
+	s := value.(string)
+	if value == nil || s == "" {
+		*tc = nil
+		return
+	}
+	err = json.Unmarshal([]byte(s), tc)
+	return
+}
+
+func (tc ToolCalls) Value() (driver.Value, error) {
+	if len(tc) == 0 {
+		return "", nil
+	}
+	jsonBytes, err := json.Marshal(tc)
+	if err != nil {
+		return "", fmt.Errorf("Could not marshal ToolCalls to JSON: %v\n", err)
+	}
+	return string(jsonBytes), nil
+}
+
+type ToolResults []api.ToolResult
+
+func (tr *ToolResults) Scan(value any) (err error) {
+	s := value.(string)
+	if value == nil || s == "" {
+		*tr = nil
+		return
+	}
+	err = json.Unmarshal([]byte(s), tr)
+	return
+}
+
+func (tr ToolResults) Value() (driver.Value, error) {
+	if len(tr) == 0 {
+		return "", nil
+	}
+	jsonBytes, err := json.Marshal([]api.ToolResult(tr))
+	if err != nil {
+		return "", fmt.Errorf("Could not marshal ToolResults to JSON: %v\n", err)
+	}
+	return string(jsonBytes), nil
+}