fix(web): fix UI bugs and unify design tokens

- Add missing .nofx-glass CSS class (used in 20+ places but undefined)
- Fix Input component referencing undefined --brand-black/--brand-light-gray
- Unify background colors to #0B0E11 (was 3 different near-blacks)
- Switch body font from IBM Plex Mono to Inter for readability
- Improve chat bubble contrast (bg 0.03→0.05, border 0.05→0.08)
- Brighten timestamp (#2c2c42→#5a5a72) and disclaimer (#1e1e32→#4a4a62)
- Unify ::selection color to gold (was orange)
- Remove global button:hover translateY that conflicted with active:scale

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/pages/AgentChatPage.tsx

@@ -630,7 +630,7 @@ export function AgentChatPage() {
       style={{
         display: 'flex',
         height: 'calc(100dvh - 64px)',
-        background: '#09090b',
+        background: '#0B0E11',
         overflow: 'hidden',
       }}
     >
@@ -655,7 +655,7 @@ export function AgentChatPage() {
             overflowX: 'auto',
             flexShrink: 0,
             backdropFilter: 'blur(12px)',
-            background: 'rgba(9,9,11,0.8)',
+            background: 'rgba(11,14,17,0.8)',
           }}
           className="hide-scrollbar"
         >