Make dashboard usable on mobile

Move inline styles into assets/style.css with wrapping KPI and chart rows,
a horizontally scrolling tab bar, and phone breakpoints. Shared components
put chart titles in HTML headings, legends above plots, and disable
drag-to-zoom so swiping scrolls the page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X9jG4CUFcH6n4vFvgtwndY

src/admin_analytics/dashboard/app.py

@@ -18,7 +18,7 @@ def create_app() -> dash.Dash:
         [
             html.H1(
                 "University of Delaware — Administrative Analytics",
-                style={"textAlign": "center", "padding": "20px", "color": "#00539F"},
+                className="app-title",
             ),
             dcc.Tabs(
                 id="tabs",
@@ -32,11 +32,12 @@ def create_app() -> dash.Dash:
                     dcc.Tab(label="Current Headcount", value="headcount"),
                     dcc.Tab(label="About", value="about"),
                 ],
-                style={"marginBottom": "20px"},
+                className="tabs-bar",
+                mobile_breakpoint=0,
             ),
-            html.Div(id="tab-content", style={"padding": "0 20px 20px 20px"}),
+            html.Div(id="tab-content", className="tab-content"),
         ],
-        style={"fontFamily": "system-ui, -apple-system, sans-serif", "maxWidth": "1400px", "margin": "0 auto"},
+        className="app",
     )
 
     @app.callback(Output("tab-content", "children"), Input("tabs", "value"))