Add native HMENU evidence for sketch promotion submenu

[coneilen]

Adds native HMENU evidence for sketch promotion. Test-only: there is no production change.

Why this was a real gap

Two existing tests bracketed the hole without covering it. The sketch-promotion test at GraphContextMenu.zig:431 is plan-only, calling promotionItems / promotionEnabled / promotionTarget without ever invoking buildMenu, so no menu is created. The native test native node menu variants expose only eligible actions does build a real menu, but only sets composite, can_arm, follows_template and unwired, and never sets sketch, so it never builds the "Promote to..." submenu.

Nothing built a real native menu containing the promotion submenu.

What the test proves

The new test calls the same private buildMenu used by show, attaches the popup to a hidden real HWND, and asserts the full three-state matrix produced by the production gating:

• not a sketch: the submenu and all three promotion commands are natively absent
• sketch with no captured context: the submenu is present and Goal, Turn and Timed are all grayed
• sketch with a captured context: the same three commands are enabled

It also pins the exact three command IDs, ordering, captions, submenu title, and command mapping. The present-but-disabled state is the one a plan-only test cannot demonstrate.

Scope

App.zig, MainWindow.zig, GraphCanvas.zig, Sidebar.zig, the test runner and the providers are all unchanged. The diff is 77 added test lines with zero deletions, plus a single ledger row.

Ledger row 100 stays Partial: only the native HMENU/HWND clause is retired. The test does not show or select a popup and does not exercise keyboard, UIA, app launch, or real-daemon acceptance and persistence, so those clauses remain.

RED: zig test src\GraphContextMenu.zig -target x86_64-windows-msvc -lc -luser32 --test-filter "sketch promotion production popup" (deliberately mutated item-count expectation 4) -> expected 4, found 3; 0 passed; 1 failed.
GREEN: zig test src\GraphContextMenu.zig -target x86_64-windows-msvc -lc -luser32 -> All 176 tests passed.
REGRESSION: zig test src\App.zig -target x86_64-windows-msvc -lc with provider and VT libraries -> All 647 tests passed.