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/PlatformsCard.tsx

@@ -57,18 +57,18 @@ export function PlatformsCard({ platforms }: PlatformsCardProps) {
                 />
 
                 <div className="flex flex-col gap-0.5 min-w-0">
-                  <span className="text-sm font-medium capitalize truncate">
+                  <span className="font-mondwest normal-case text-sm font-medium capitalize truncate">
                     {name}
                   </span>
 
                   {info.error_message && (
-                    <span className="text-xs text-destructive">
+                    <span className="font-mondwest normal-case text-xs text-destructive">
                       {info.error_message}
                     </span>
                   )}
 
                   {info.updated_at && (
-                    <span className="text-xs text-muted-foreground">
+                    <span className="font-mondwest normal-case text-xs text-muted-foreground">
                       {t.status.lastUpdate}: {isoTimeAgo(info.updated_at)}
                     </span>
                   )}