internal/app: unexport outcome, remove app struct

The App struct no longer does anything, and the outcome struct is entirely opaque.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/app/strings.go

@@ -2,12 +2,9 @@ package app
 
 import (
 	"strconv"
-
-	"hakurei.app/internal/app/state"
 )
 
-func newInt(v int) *stringPair[int]            { return &stringPair[int]{v, strconv.Itoa(v)} }
-func newID(id *state.ID) *stringPair[state.ID] { return &stringPair[state.ID]{*id, id.String()} }
+func newInt(v int) *stringPair[int] { return &stringPair[int]{v, strconv.Itoa(v)} }
 
 // stringPair stores a value and its string representation.
 type stringPair[T comparable] struct {