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/ChatSidebar.tsx

@@ -304,13 +304,13 @@ export function ChatSidebar({ channel, className }: ChatSidebarProps) {
   return (
     <aside
       className={cn(
-        "flex h-full w-full min-w-0 shrink-0 flex-col gap-3 overflow-y-auto overflow-x-hidden pr-1 normal-case lg:w-80",
+        "flex h-full w-full min-w-0 shrink-0 flex-col gap-3 overflow-y-auto overflow-x-hidden pr-1 lg:w-80",
         className,
       )}
     >
       <Card className="flex items-center justify-between gap-2 px-3 py-2">
         <div className="min-w-0">
-          <div className="text-xs uppercase tracking-wider text-muted-foreground">
+          <div className="text-display text-xs tracking-wider text-text-tertiary">
             model
           </div>
 
@@ -321,7 +321,7 @@ export function ChatSidebar({ channel, className }: ChatSidebarProps) {
             onClick={() => setModelOpen(true)}
             suffix={
               canPickModel ? (
-                <ChevronDown className="opacity-60" />
+                <ChevronDown className="text-text-secondary" />
               ) : undefined
             }
             className="self-start min-w-0 px-0 py-0 normal-case tracking-normal text-sm font-medium hover:underline disabled:no-underline"
@@ -357,13 +357,13 @@ export function ChatSidebar({ channel, className }: ChatSidebarProps) {
       )}
 
       <Card className="flex min-h-0 flex-none flex-col px-2 py-2">
-        <div className="px-1 pb-2 text-xs uppercase tracking-wider text-muted-foreground">
+        <div className="text-display px-1 pb-2 text-xs tracking-wider text-text-tertiary">
           tools
         </div>
 
         <div className="flex min-h-0 flex-col gap-1.5">
           {tools.length === 0 ? (
-            <div className="px-2 py-4 text-center text-xs text-muted-foreground">
+            <div className="px-2 py-4 text-center text-xs text-text-secondary">
               no tool calls yet
             </div>
           ) : (