T23c: AI chat, input

- PromptInput: attachments and context above the field, the owner's tools and
  send below; Enter sends, Shift-Enter breaks the line; / offers commands and
  @ offers context over forms::Suggestions; files dropped on it attach behind a
  drop veil
- AttachmentButton, AttachmentChip with thumbnails and uploads, ContextChips
- VoiceInputButton and VoiceWaveform with a red dot and the time
- ParameterPanel, SystemPromptEditor, TokenCounter, CostEstimator
- forms: a Newline action on Shift-Enter keeps one-line fields to one line;
  replace_trigger moves beside Suggestions; choose and dropped shared
- gallery: composer, pickers and tuning

tasks/ch21-30.md

@@ -121,27 +121,27 @@
 
 ## T23c AI Chat · Input
 
-- [ ] PromptInput / Composer
-- [ ] AttachmentButton
-- [ ] AttachmentChip / AttachmentPreview
-- [ ] PasteImagePreview
-- [ ] DragDropOverlay
-- [ ] VoiceInputButton
-- [ ] VoiceWaveform / RecordingIndicator
-- [ ] SlashCommandMenu → `documents::SlashMenu`
-- [ ] PromptTemplateMenu
-- [ ] ContextMentionMenu
-- [ ] ContextChips
-- [ ] ModelSelector
-- [ ] ModeSelector
-- [ ] ToolToggleMenu
-- [ ] TemperatureSlider / ParameterPanel
-- [ ] SystemPromptEditor
-- [ ] TokenCounter
-- [ ] ContextWindowMeter
-- [ ] CostEstimator
-- [ ] SendButton
-- [ ] InputHint
+- [x] PromptInput / Composer → `chat::PromptInput`
+- [x] AttachmentButton
+- [x] AttachmentChip / AttachmentPreview → `chat::AttachmentChip`, a picture's thumbnail or a file's icon
+- [x] PasteImagePreview → a pasted picture as an `AttachmentChip`
+- [x] DragDropOverlay
+- [x] VoiceInputButton
+- [x] VoiceWaveform / RecordingIndicator → `chat::VoiceWaveform`, a red dot and the time with the bars
+- [x] SlashCommandMenu → `/` at the start of `chat::PromptInput`, over `forms::Suggestions`
+- [x] PromptTemplateMenu → `menus::DropdownMenu` of saved prompts
+- [x] ContextMentionMenu → `@` in `chat::PromptInput`
+- [x] ContextChips
+- [x] ModelSelector → `forms::Select`, a note on each model
+- [x] ModeSelector → `buttons::SegmentedControl`
+- [x] ToolToggleMenu → `menus::DropdownMenu` with check rows
+- [x] TemperatureSlider / ParameterPanel → `chat::ParameterPanel`
+- [x] SystemPromptEditor
+- [x] TokenCounter
+- [x] ContextWindowMeter → `data_display::UsageBar`
+- [x] CostEstimator
+- [x] SendButton
+- [x] InputHint
 
 ## T23d AI Chat · Conversations