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

src/chat/mod.rs

@@ -1,30 +1,38 @@
 mod actions;
+mod attach;
 mod cite;
 mod code;
+mod composer;
 mod list;
 mod media;
 mod message;
+mod params;
 mod play;
 mod search;
 mod status;
 mod stream;
 #[cfg(all(test, feature = "test-support"))]
 mod tests;
+mod voice;
 
 pub use actions::{
     BranchNavigator, MessageActions, MessageEditor, QuoteReply, continue_button, regenerate_button,
     stop_button,
 };
+pub use attach::{Attachment, AttachmentChip, ContextChips};
 pub use cite::{CitationBadge, Source, SourceCard, SourceList};
 pub use code::CodeBlock;
+pub use composer::{AttachmentButton, DragDropOverlay, InputHint, PromptInput, SendButton};
 pub use list::{DateSeparator, MessageList, ScrollToBottomButton};
 pub use media::{FileMessage, ImageGrid, ImageMessage, LinkPreviewCard};
 pub use message::{
     ChatContainer, MessageAvatar, MessageBubble, MessageFooter, MessageHeader, Role,
 };
+pub use params::{CostEstimator, Parameter, ParameterPanel, SystemPromptEditor, TokenCounter};
 pub use play::{AudioMessage, VideoMessage};
 pub use search::{DocumentChunkPreview, SearchProgress, StepState, WebResultCard};
 pub use status::{
     ErrorMessage, FeedbackForm, RateLimitNotice, ThinkingBlock, ThinkingDuration, ThinkingIndicator,
 };
 pub use stream::{StreamingCursor, StreamingMarkdown, StreamingText};
+pub use voice::{VoiceInputButton, VoiceWaveform};