Fixed styling guidance in CLAUDE.md and frontend rules.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.claude/rules/frontend.md

@@ -6,6 +6,7 @@ paths:
   - "src/app.rs"
   - "src/validator.rs"
   - "style/**"
+  - "assets/css/**"
 ---
 
 # Frontend rules
@@ -44,6 +45,6 @@ paths:
 ## Styling
 
 - UI is the Bootstrap-based admin template in `assets/vendor/` plus Boxicons (`<i class="bx bx-...">`). Reuse its classes (`card`, `table`, `btn btn-primary`, `form-control`, `row`/`col`) before writing CSS.
-- Custom styles go to `style/main.scss`. Never edit `assets/vendor/`.
+- Custom styles go to a CSS file in `assets/css/` and must be linked with `<Link rel="stylesheet">` in `src/components/header.rs` (order matters: after the vendor files to override them). `style/main.scss` is not linked anywhere and has no effect. Never edit `assets/vendor/` (the one app-owned file there is `assets/vendor/css/control.css`).
 - The public page banner style is `assets/data/banner.css`, rewritten at runtime by the appearance upload (`/*bg-img*/` marker) — keep that marker / the `background-image: url('...')` form intact.
 - Stylesheets and meta tags are declared in `src/components/header.rs`.