T25a Generative: prompt and settings

PromptEnhancer offers a fuller prompt with the words it adds washed,
split at punctuation; Use this takes it into the field, Keep mine
lets it go. StylePresetPicker and AspectRatioPicker are rows of Tab
stops, the chosen one in accent; a ratio chip draws its shape.
SeedInput keeps digits up to u32::MAX and rolls one with a die.
NegativePromptInput and ImageGenerationPanel point to forms::TagInput
and forms::Form. theme.generative() holds the chapter's sizes. The
gallery's preset pictures are the atrium photo in five styles.

src/lib.rs

@@ -12,6 +12,7 @@ pub mod editor;
 pub mod feedback;
 pub mod finance;
 pub mod forms;
+pub mod generative;
 pub mod git;
 pub mod layout;
 pub mod lists;