TUI refactor

- Clean up, improved startup logic, initial conversation load
- Moved converation/message business logic (mostly) into `model/tui`

pkg/tui/shared/shared.go

@@ -1,17 +1,10 @@
 package shared
 
 import (
-	"git.mlow.ca/mlow/lmcli/pkg/lmcli"
 	tea "github.com/charmbracelet/bubbletea"
 )
 
-type Values struct {
-	ConvShortname string
-}
-
 type Shared struct {
-	Ctx    *lmcli.Context
-	Values *Values
 	Width  int
 	Height int
 	Err    error