fix(frontend): resolve Vite assets by manifest source path (#37836)

In dev mode `/api/swagger` returned HTTP 500 (`Failed to locate local
path for managed asset URI: css/swagger.css`): the backend synthesised
asset keys from the Vite entry name instead of reading the manifest,
which only worked by coincidence and broke once a source file name
diverged from its entry name.

This keys the manifest by its source path (e.g. `web_src/js/index.ts`)
and resolves entries directly — hashed `file` in prod, dev-server source
in dev. A new `AssetCSSLinks` helper renders a JS entry's stylesheet
`<link>` tags from the manifest (the entry's CSS plus the CSS of its
statically-imported chunks).

Fixes: https://github.com/go-gitea/gitea/issues/37830
Fixes: https://github.com/go-gitea/gitea/pull/37832
Fixes: https://github.com/go-gitea/gitea/pull/37876
Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: prakhar0x01 <prakharporwal2004@gmail.com>
Co-authored-by: Nicolas <bircni@icloud.com>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: Giteabot <teabot@gitea.io>

modules/markup/render.go

@@ -243,7 +243,7 @@ func RenderWithRenderer(ctx *RenderContext, renderer Renderer, input io.Reader,
 			return RenderIFrame(ctx, &extOpts, output)
 		}
 		// else: this is a standalone page, fallthrough to the real rendering, and add extra JS/CSS
-		extraScriptSrc := public.AssetURI("js/external-render-helper.js")
+		extraScriptSrc := public.AssetURI("web_src/js/external-render-helper.ts")
 		extraLinkHref := ctx.RenderOptions.StandalonePageOptions.CurrentWebTheme.PublicAssetURI()
 		// "<script>" must go before "<link>", to make Golang's http.DetectContentType() can still recognize the content as "text/html"
 		// DO NOT use "type=module", the script must run as early as possible, to set up the environment in the iframe