Count clicks ourselves so double-clicks work at all

Pixi only fills `detail` on the `click` event it synthesises; on
`pointerdown` it is always 0, so every `e.detail === 2` branch was dead
code. Asset rows, hierarchy folding and select-all in text fields never
responded to a double-click.

A shared click counter in src/ui/clicks.ts replaces the three readings of
`e.detail`. A finished double-click ends the run, so two in a row count
2 and 2 rather than 3 and 4.

The harness could only send `clickCount: 1`, which is why no test caught
this: every "activate" check went through Enter. It can send real
double-clicks now, and five checks drive the three paths separately.

src/editor/debugHook.ts

@@ -181,6 +181,8 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
     /** Rows the hierarchy shows – collapsed subtrees are not in here. */
     hierarchyOrder: () => hierarchy.rowOrder(),
     hierarchyChevron: (id: string) => hierarchy.chevronPosition(id),
+    /** Centre of a hierarchy row, clear of the chevron – for clicks that must hit the row itself. */
+    hierarchyRow: (id: string) => hierarchy.rowPosition(id),
     hierarchyRowColor: (id: string) => hierarchy.rowColor(id),
     hierarchyExpandAll: () => hierarchy.expandAll(),
     hierarchyCollapseAll: () => hierarchy.collapseAll(),