More monior TUI refactor/cleanup

`tui/tui.go` is no longer responsible for passing window resize updates
to all views, instead we request a new window size message to be sent at
the same time we enter the view, allowing the view to catch and handle
it.

Add `Initialized` to `tui/shared/View` model, now we only call
`Init` on a view before entering it for the first time, rather than
calling `Init` on all views when the application starts.

Renames file, small cleanups

pkg/tui/shared/shared.go

@@ -5,6 +5,7 @@ import (
 )
 
 type Shared struct {
+	Initialized bool
 	Width  int
 	Height int
 	Err    error
@@ -29,6 +30,12 @@ type (
 	MsgError error
 )
 
+func ViewEnter() tea.Cmd {
+	return func() tea.Msg {
+		return MsgViewEnter{}
+	}
+}
+
 func WrapError(err error) tea.Cmd {
 	return func() tea.Msg {
 		return MsgError(err)