feat(caption): let live captions use their own speech model

The speech engine now keeps an auxiliary model next to the dictation model
and transcribes with whichever the request names, reloading it once if the
engine restarted. Settings > STT gains a live-caption model so captions can
run on large-v3-turbo while dictation keeps its own model. The runtime
minimum rises to 1.7.0 because older engines would silently ignore the
model choice.

Suggestion paging moves to Up/Down: the page follows the selection and the
last item waits while more candidates are being generated. The Left/Right
page shortcuts are removed; they did nothing until a page had filled and
clash with Intel's display-rotation hotkeys.

CHANGELOG.md

@@ -15,6 +15,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **Captions are polished in context.** Each finished line is corrected by the local
   model using the lines before it (spacing, punctuation, misheard words); rewrites
   that change too much are ignored. It can be turned off in Settings.
+- **Live captions can use their own speech model.** Settings > STT now has a separate
+  live-caption model, loaded next to the dictation model, so captions can run on a
+  faster or more accurate model without changing dictation. The local speech engine
+  is updated for this and is downloaded again once.
+
+### Changed
+- **Suggestions page with Up/Down only.** Moving past the third candidate turns the
+  page by itself, and at the last candidate the selection waits while more are still
+  being generated. The separate Ctrl+Alt+Left/Right page shortcuts are gone; they also
+  collided with the display-rotation shortcut of Intel graphics drivers.
 
 ### Planned
 - macOS / Linux support