feat(theme): resolve state precedence - #49813

What

Add state(flags) to every resolved action and form-field color:

theme.background.action.primary.default

theme.background.action.primary.state({
  disabled: disabled(),
  pressed: pressed(),
  focused: focused(),
  selected: selected(),
  hovered: hovered(),
})

The first active state in ActionState.literals wins:

disabled > pressed > focused > selected > hovered > default

Missing and false flags are ignored. If every property is false or absent, state() returns the existing default color.

The API is available consistently on:

• theme.text.action.<variant>
• theme.background.action.<variant>
• theme.text.formfield
• theme.background.formfield
• plugin context.theme, because it receives the same ResolvedTheme shape

Existing direct property access remains unchanged (primary.focused, formfield.selected, etc.). This PR only adds the resolver; production call sites will migrate separately.

Verification

• bun run typecheck in packages/theme
• bun run typecheck in packages/tui
• bun test in packages/theme (6 pass)
• focused TUI theme tests (21 pass)
• tests cover every precedence level, all-false fallback, and form-field availability