fix(maestro): keep accent fill when previewing active row

Hovering the session already in the pane put the preview tint over its accent fill, so the row that is on screen looked unpicked. Tier 5 now skips `.is-active`.

docs/PREVIEW.md

@@ -46,7 +46,7 @@ Web client (`--preview` and friends in `web/src/styles.css`):
 | The previewed pane's titlebar | Tinted in the preview hue, at full strength, in place of the focused pane's accent tint. |
 | The canvas | A `preview` chip, top right, and a dashed inset ring. |
 | A throwaway tab | Dashed border, italic label. |
-| The sidebar row being previewed | Filled with the preview hue, over whatever open/focused state the row already had. |
+| The sidebar row being previewed | Filled with the preview hue, over whatever open state the row already had — but the row of the session already showing in the pane keeps its accent fill, since previewing it changes nothing on screen. |
 | A hovered sidebar row, and the keyboard cursor on a session | A lighter wash of the same hue, because both are what previews a row. |
 
 Rows say it with fill, not with an edge — see the tier ladder in

docs/SIDEBAR.md

@@ -189,7 +189,7 @@ furthest down wins the paint.
 | Under the pointer or the keyboard walk | preview hue, light | selection surface, while the sidebar holds the keyboard |
 | Open in some pane, not the focused one | 6% accent wash (`.is-open`) | — (the `●` glyph carries it) |
 | Showing in the pane | `--accent-fill` | `pane_row_bg()` — partway from the card surface to the selection surface |
-| Previewing (`docs/PREVIEW.md`) | `--preview-tint` | — (no preview colour role yet) |
+| Previewing (`docs/PREVIEW.md`), unless that row is the one showing in the pane | `--preview-tint` | — (no preview colour role yet) |
 
 The web ladder is written as one ordered run of equal-specificity rules in
 `styles.css`, every qualifier inside `:where()`, so the order they appear in