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/SidebarFooter.tsx

@@ -16,8 +16,7 @@ export function SidebarFooter() {
       )}
     >
       <Typography
-        mondwest
-        className="font-mono-ui text-[0.7rem] tabular-nums tracking-[0.1em] text-muted-foreground/70 lowercase"
+        className="font-mono-ui text-xs tabular-nums tracking-[0.08em] text-text-tertiary lowercase"
       >
         {status?.version != null ? `v${status.version}` : "—"}
       </Typography>
@@ -27,7 +26,7 @@ export function SidebarFooter() {
         target="_blank"
         rel="noopener noreferrer"
         className={cn(
-          "font-mondwest text-[0.65rem] tracking-[0.15em] text-midground",
+          "font-mondwest text-display text-xs tracking-[0.12em] text-midground",
           "transition-opacity hover:opacity-90",
           "focus-visible:rounded-sm focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-midground/40",
         )}