T25d Generative: sound and motion

AudioGenerationPlayer shows a generated sound's prompt, model and
length, a bar while it is made, then chat::AudioMessage to play it;
Regenerate and Download wait for it. TTSVoicePicker lists voices with a
sample to play, the chosen one washed with a check, tags dropping below
when narrow. VideoGenerationTimeline lays shots along their time under
a ruler, with posters, placeholders, a playhead and Extend.

AudioMessage's waveform is one Tab stop where Left and Right seek, and
it gives way at 280px. debug::ruler serves the timeline's ruler. A mask
shown to read no longer follows the pointer.

src/debug/mod.rs

@@ -19,6 +19,7 @@ pub use hex::HexViewer;
 pub use network::{NetworkInspector, Request};
 pub use session::{Breakpoint, BreakpointList, DebugCommand, DebugState, DebugToolbar};
 pub use stack::{CallStack, StackFrame, Thread, ThreadList, ThreadState};
+pub(crate) use timeline::ruler;
 pub use timeline::{Span, TimelineProfiler, zoomed};
 pub use variables::{ValueKind, Variable, VariablesPanel, Watch, WatchPanel};