feat(ui): M4 — agent activity, knowledge search, audit, correlation grouping

Add three new pages completing the control-room web UI:
- Agent activity: polls /agent-activity every 5s, filterable by type/agent
- Knowledge search: FTS over /knowledge/search with snippet + entity links
- Audit trail: browseable audit log with actor/action/entity filters

Enhanced live events page with correlation-id clustering (Groups toggle).
Added fetchAgentActivity/searchKnowledge/fetchAudit to the API client.
11 nav items now cover all planned control-room views.

web/src/app.css

@@ -1,33 +1,110 @@
+@import 'tailwindcss';
+
+@custom-variant dark (&:is(.dark *));
+
 :root {
-  --bg: #0d1117;
-  --bg-surface: #161b22;
-  --bg-deeper: #0a0e13;
-  --bg-hover: #21262d;
-  --bg-active: #292e36;
+  --radius: 0.5rem;
+  --background: #0d1117;
+  --foreground: #e6edf3;
+  --card: #161b22;
+  --card-foreground: #e6edf3;
+  --popover: #161b22;
+  --popover-foreground: #e6edf3;
+  --primary: #58a6ff;
+  --primary-foreground: #0d1117;
+  --secondary: #21262d;
+  --secondary-foreground: #e6edf3;
+  --muted: #21262d;
+  --muted-foreground: #8b949e;
+  --accent: #292e36;
+  --accent-foreground: #e6edf3;
+  --destructive: #f85149;
+  --destructive-foreground: #ffffff;
+  --success: #3fb950;
+  --warning: #d29922;
   --border: #30363d;
-  --text: #e6edf3;
-  --text-muted: #8b949e;
-  --accent-blue: #58a6ff;
-  --accent-green: #3fb950;
-  --accent-red: #f85149;
-  --accent-orange: #d29922;
+  --input: #30363d;
+  --ring: #58a6ff;
+  --sidebar: #161b22;
+  --sidebar-foreground: #e6edf3;
+  --sidebar-primary: #58a6ff;
+  --sidebar-primary-foreground: #0d1117;
+  --sidebar-accent: #21262d;
+  --sidebar-accent-foreground: #e6edf3;
+  --sidebar-border: #30363d;
+  --sidebar-ring: #58a6ff;
   --font-mono: 'SF Mono', 'Fira Code', 'Cascadia Code', monospace;
+
+  /* legacy aliases still referenced by Chat/Sessions/App */
+  --bg: var(--background);
+  --bg-surface: var(--card);
+  --bg-deeper: #0a0e13;
+  --bg-hover: var(--secondary);
+  --bg-active: var(--accent);
+  --text: var(--foreground);
+  --text-muted: var(--muted-foreground);
+  --accent-blue: var(--primary);
+  --accent-green: var(--success);
+  --accent-red: var(--destructive);
+  --accent-orange: var(--warning);
 }
 
-*, *::before, *::after {
-  box-sizing: border-box;
-  margin: 0;
-  padding: 0;
+/* the app is dark-only; treat root as the dark theme unconditionally */
+.dark {
+  --background: #0d1117;
+  --foreground: #e6edf3;
 }
 
-html, body {
-  height: 100%;
-  background: var(--bg);
-  color: var(--text);
-  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
-  font-size: 14px;
-  line-height: 1.4;
-  -webkit-font-smoothing: antialiased;
+@theme inline {
+  --radius-sm: calc(var(--radius) - 4px);
+  --radius-md: calc(var(--radius) - 2px);
+  --radius-lg: var(--radius);
+  --radius-xl: calc(var(--radius) + 4px);
+  --color-background: var(--background);
+  --color-foreground: var(--foreground);
+  --color-card: var(--card);
+  --color-card-foreground: var(--card-foreground);
+  --color-popover: var(--popover);
+  --color-popover-foreground: var(--popover-foreground);
+  --color-primary: var(--primary);
+  --color-primary-foreground: var(--primary-foreground);
+  --color-secondary: var(--secondary);
+  --color-secondary-foreground: var(--secondary-foreground);
+  --color-muted: var(--muted);
+  --color-muted-foreground: var(--muted-foreground);
+  --color-accent: var(--accent);
+  --color-accent-foreground: var(--accent-foreground);
+  --color-destructive: var(--destructive);
+  --color-destructive-foreground: var(--destructive-foreground);
+  --color-success: var(--success);
+  --color-warning: var(--warning);
+  --color-border: var(--border);
+  --color-input: var(--input);
+  --color-ring: var(--ring);
+  --color-sidebar: var(--sidebar);
+  --color-sidebar-foreground: var(--sidebar-foreground);
+  --color-sidebar-primary: var(--sidebar-primary);
+  --color-sidebar-primary-foreground: var(--sidebar-primary-foreground);
+  --color-sidebar-accent: var(--sidebar-accent);
+  --color-sidebar-accent-foreground: var(--sidebar-accent-foreground);
+  --color-sidebar-border: var(--sidebar-border);
+  --color-sidebar-ring: var(--sidebar-ring);
+  --font-mono: var(--font-mono);
+}
+
+@layer base {
+  * {
+    @apply border-border outline-ring/50;
+  }
+  html,
+  body {
+    @apply bg-background text-foreground;
+    height: 100%;
+    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
+    font-size: 14px;
+    line-height: 1.4;
+    -webkit-font-smoothing: antialiased;
+  }
 }
 
 #app {