docs(f6): any-file behavior + Ctrl+Alt+D wording (#19)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/MANUAL-SMOKE-F6.md

@@ -6,10 +6,11 @@ rest of F6 needs no credentials and no network.
 
 1. `npm run build`, launch the extension (F5 in VS Code opens the committed
    `sandbox/` playground), open `playground.md`.
-2. Edit a sentence by hand, then **Cmd/Ctrl-Alt-D** (or run **Cowriting: Toggle
-   Diff View**). ✅ A diff opens: the readonly baseline on the left, your live
-   document on the right; the tab title reads `playground.md — my changes since
-   opened <time>`. Your hand edit shows as a change.
+2. Edit a sentence by hand, then **`Ctrl+Alt+D`** (same chord on macOS — not
+   `Cmd`; or run **Cowriting: Toggle Diff View**). ✅ A diff opens: the readonly
+   baseline on the left, your live document on the right; the tab title reads
+   `playground.md — my changes since opened <time>`. Your hand edit shows as a
+   change.
 3. Keep typing **in the diff's right pane**. ✅ Editing continues in place;
    decorations/threads still work. Toggle again. ✅ The diff tab closes and the
    normal editor is back.
@@ -21,6 +22,9 @@ rest of F6 needs no credentials and no network.
    now); the title reads `pinned <time>`. Type → your changes show against the
    pin.
 6. Reload the window (Developer: Reload Window). ✅ Toggle: the baseline is the
-   same as before the reload (persisted in workspace storage, not the repo —
-   INV-19; `git status` shows nothing new).
-7. Toggle on a file outside the workspace folder. ✅ A warning, no diff.
+   same as before the reload (persisted in **global** extension storage, not the
+   repo — INV-19; `git status` shows nothing new).
+7. **Any file (#19):** open a file from *outside* the `sandbox/` folder, or a
+   new untitled buffer (`Cmd/Ctrl+N`), edit it, and `Ctrl+Alt+D`. ✅ The diff
+   opens there too — untitled buffers show `(unsaved)` in the title and diff
+   in-memory. Toggle with focus on a non-editor (e.g. the terminal) → warning.