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.

TASKS.md

@@ -83,7 +83,12 @@ Per-component lines live in `tasks/`. Tags there:
 - [x] T24d Agent · Previews
 - [x] T24e Agent · Environment
 - [x] T24f Agent · Control and cost
-- [ ] T25 Generative
+- [ ] T25a Generative · Prompt and settings
+- [ ] T25b Generative · Queue and results
+- [ ] T25c Generative · Canvas
+- [ ] T25d Generative · Sound and motion
+- [ ] T25e Generative · Models
+- [ ] T25f Generative · Data and prompts
 - [ ] T26 Media
 - [ ] T27 Files
 - [ ] T28 Messaging