fix(embed): include underscore-prefixed Vite chunks in dist FS

go:embed silently excludes files whose names start with `_` or `.`,
so the `_plugin-vue_export-helper-<hash>.js` chunk that Vite/rolldown
emits for @vitejs/plugin-vue was missing from the production binary.
First import at runtime hit a 404 and the SPA failed to mount — blank
page on every page load, no error in the server logs because the
asset 404 was just a static-handler miss.

Switched the directive to `//go:embed all:dist` which keeps the same
root layout but disables the underscore/dot exclusion rule. Dev mode
was unaffected (it serves dist/assets/ from disk, not the embedded FS).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/web.go

@@ -41,7 +41,13 @@ var i18nFS embed.FS
 // HTML route is served straight out of this FS — the legacy Go
 // templates and `web/assets/` tree are gone post-Phase 8.
 //
-//go:embed dist/*
+// `all:` is required so files whose names start with `_` are NOT
+// silently excluded by go:embed's default rules. Vite/rolldown emits
+// `_plugin-vue_export-helper-<hash>.js` for the @vitejs/plugin-vue
+// runtime; without `all:` the chunk would be missing from the binary
+// at runtime → 404 → blank-page boot failure.
+//
+//go:embed all:dist
 var distFS embed.FS
 
 var startTime = time.Now()