Frontend: Add browser capabilities check #5047

Signed-off-by: Michael Mayer <michael@photoprism.app>

CODEMAP.md

@@ -1,6 +1,6 @@
 PhotoPrism — Backend CODEMAP
 
-**Last Updated:** October 4, 2025
+**Last Updated:** October 11, 2025
 
 Purpose
 - Give agents and contributors a fast, reliable map of where things live and how they fit together, so you can add features, fix bugs, and write tests without spelunking.
@@ -42,6 +42,12 @@ High-Level Package Map (Go)
 - `internal/ffmpeg`, `internal/thumb`, `internal/meta`, `internal/form`, `internal/mutex` — media, thumbs, metadata, forms, coordination
 - `pkg/*` — reusable utilities (must never import from `internal/*`), e.g. `pkg/fs`, `pkg/log`, `pkg/service/http/header`
 
+Templates & Static Assets
+- Entry HTML lives in `assets/templates/index.gohtml`, which includes the splash markup from `app.gohtml` and the SPA loader from `app.js.gohtml`.
+- The loader script is implemented in `assets/static/js/app-loader.js` (included via `app.js.gohtml`) and performs capability checks (Promise, fetch, AbortController, `script.noModule`, etc.) before injecting `window.__CONFIG__.jsUri`. Update this file (and the partial) in lockstep with the templates in private repos (`pro/assets/templates/index.gohtml`, `plus/assets/templates/index.gohtml`) because they import the same partial.
+- `splash.gohtml` renders the loading screen text while the bundle loads; styles are in `frontend/src/css/splash.css`.
+- When adjusting browser support messaging, update both the loader partial and splash styles so the warning message stays consistent across editions.
+
 HTTP API
 - Handlers live in `internal/api/*.go` and are registered in `internal/server/routes.go`.
 - Annotate new endpoints in handler files; generate docs with: `make fmt-go swag-fmt && make swag`.