fix: keep all tabs mounted, switch via CSS display instead of unmount

All 4 tabs (Dashboard, Studio, Shell, Config) are now always mounted
and toggled via .tab-hidden (display:none). This preserves:
- Dashboard graph history across tab switches
- Terminal session state and progress
- Studio chat context
- Config form state

Dashboard polling pauses after 3 ticks when hidden to save resources
and auto-resumes when the tab becomes visible again.

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

web/src/styles/global.css

@@ -154,7 +154,8 @@ input::placeholder { color: var(--text-disabled); }
 
 .header-clock { font-family: var(--font-mono); font-size: 12px; color: var(--accent); font-weight: 600; }
 
-.content { flex: 1; overflow: hidden; }
+.content { flex: 1; overflow: hidden; position: relative; }
+.tab-hidden { display: none; }
 
 .statusbar {
   height: 28px;
@@ -606,10 +607,10 @@ input::placeholder { color: var(--text-disabled); }
 }
 .dash-proc-name {
   font-size: 11px; font-weight: 600; color: var(--text-primary);
-  font-family: var(--font-mono);
+  font-family: var(--font-mono); flex: 1; min-width: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap;
 }
 .dash-proc-res {
-  font-size: 10px; font-family: var(--font-mono); color: var(--text-tertiary);
+  font-size: 10px; font-family: var(--font-mono); color: var(--text-tertiary); flex-shrink: 0;
 }
 
 /* Commands */