system.php: extract inline JS and style= attrs into separate assets

Move the ~130-line $extraJsInline heredoc from admin/system.php into a
static file public/assets/js/system.js, loaded via $extraJs so the
template footer emits a normal <script src=…>.

Replace 4 inline style= attributes with named CSS modifier classes in
system.css:
  - style="margin:0;border:none;padding:0" on .srv-section-title
    → .srv-section-title--compact
  - style="margin-bottom:.75rem" on sub-heading <h3>
    → .srv-section-title--sub
  - style="margin-bottom:0" on .php-grid
    → .php-grid--flush
  - style="font-size:.84rem;color:var(--text-secondary)" on <label>
    → .log-toolbar label rule in system.css

The one remaining inline style (--disk-pct / --disk-color CSS custom
properties on .disk-bar) is intentionally kept: it carries PHP runtime
values that cannot be expressed in a static stylesheet.

todo/01-css-semantic-refactor.md

@@ -18,6 +18,7 @@
 - [x] **`tfe.css`**: Replace `.tfe-file-caption` with `aside figcaption` — already done
 - [x] **`search.css`**: Replace `.repertoire-col > h2` — already uses `.repertoire-index section > h2`
 - [x] **`system.php`**: Move inline `<style>` block to `system.css`
+- [x] **`system.php`**: Extract `$extraJsInline` JS block to `public/assets/js/system.js`; replace remaining inline `style=` attributes with CSS modifier classes (`.srv-section-title--compact`, `.srv-section-title--sub`, `.php-grid--flush`, `.log-toolbar label`)
 
 ## Template HTML changes to match