refactor(web): dashboard typography & contrast pass

Removes the global `uppercase` + `font-mondwest` from the App.tsx root
that forced every page to opt-out, replaces stacked-alpha text colors
with semantic tokens for WCAG-AA contrast across all 7 themes, and
applies the new `text-display` utility from @nous-research/ui@0.16.0
on intentional brand chrome (page titles, sidebar headings, segmented
filters) only. Bumps every sub-12px arbitrary text size to text-xs.

Also widens the dashboard plugin routes (/api/dashboard/agent-plugins/
{name:path}/...) so category-namespaced plugins like observability/
langfuse and image_gen/openai can be enable/disabled from the dashboard
— previously the FE encodeURIComponent-ed the slash and the backend
{name} route rejected it. _validate_plugin_name still blocks .. and
backslash, and strips leading/trailing slash.

Touches sessions/env/keys page chrome and adds two new i18n keys
(`overview`, `showMore`/`showLess`) across all 18 locales.

Squashes 19 commits from PR #28832.

Co-authored-by: Hermes <noreply@nousresearch.com>

web/src/components/SidebarStatusStrip.tsx

@@ -27,21 +27,21 @@ export function SidebarStatusStrip() {
       className={cn(
         "block text-left",
         "px-5 pb-2 pt-0.5",
-        "text-muted-foreground/70",
-        "transition-colors hover:text-muted-foreground/90",
+        "text-text-secondary",
+        "transition-colors hover:text-midground",
         "focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-midground/40",
         "focus-visible:ring-inset",
       )}
     >
-      <div className="flex flex-col gap-1 font-mondwest text-[0.55rem] leading-snug tracking-[0.12em]">
+      <div className="flex flex-col gap-1 font-mondwest text-xs leading-snug tracking-[0.08em]">
         <p className="break-words">
-          <span className="text-muted-foreground/50">{gatewayStatusLabel}</span>{" "}
+          <span className="text-text-tertiary">{gatewayStatusLabel}</span>{" "}
           <span className={cn("font-medium", gw.tone)}>{gw.label}</span>
         </p>
 
         <p className="break-words">
-          <span className="text-muted-foreground/50">{activeSessionsLabel}</span>{" "}
-          <span className="tabular-nums text-muted-foreground/70">
+          <span className="text-text-tertiary">{activeSessionsLabel}</span>{" "}
+          <span className="tabular-nums text-text-secondary">
             {status.active_sessions}
           </span>
         </p>