feat(extract): discover Razor Pages / MVC views (.cshtml) and route their @page

[DeusData]

Follow-up to #1824 (thanks @The1nk), which mapped Blazor .razor to the C# host and extracted @page routes from it. This extends the same treatment to the rest of the Razor family, and stops there.

Why .cshtml specifically

.cshtml is the same Razor syntax with the same C# host, and it was equally unmapped — an ASP.NET Core MVC or Razor Pages application produced no nodes at all for its entire view tree.

@page matters more here than it does for components. On a Blazor component the directive is an optional annotation; in Razor Pages it is the directive that defines a page, so the routable surface of a Razor Pages app lives exclusively in this file type.

The extension mapping alone would not have worked

cbm_path_is_razor() hardcoded a single .razor suffix. Adding {".cshtml", CBM_LANG_CSHARP} to the extension table would have given .cshtml discovery and parsing but left it skipped by the directive scan — files present in the graph with none of their routes, which is the more confusing of the two failure modes. The gate is now a suffix table covering both.

Scope: the Razor family only

• .vbhtml — excluded. There is no VB.NET language in this repo, so there is no host to map it to.
• .aspx / .ascx — excluded. Web Forms is a different templating syntax (<%@ %>, runat="server") with no @page directive, so neither the C# error recovery nor the directive scan applies. Mapping them would produce parse noise and no routes.

Best-effort on the same terms as .razor: the C# grammar recovers the @{ } and @functions blocks, and the surrounding markup lands in ERROR regions reported through parse_partial.

Tests

• lang_ext_cshtml — the extension mapping.
• extract_razor_page_directive_routes_cshtml_view — a Pages/Orders/Index.cshtml with @page "/orders", asserting the extracted route path and method.
• extract_razor_layout_without_page_has_no_route — a Pages/Shared/_Layout.cshtml, asserting no Route node. Most .cshtml files are layouts and partials; a spurious Route per view would be worse than the missing ones this fixes.

Local: language + extraction suites pass (566), lint-ci clean.