feat: Learning page — capability timeline + trend, built on real data

The plan's "learning view" (runbook success-rate trends, promoted
skills, capability timeline) assumes the patterns/skills/feedback
pipeline is populated. It isn't: all three tables are empty in
production and nothing in the codebase ever writes to feedback, so
building the UI against them today would ship a permanently-empty
page. Scoped instead around data that's real and growing —
executions — while still wiring up /patterns and /skills so the page
needs no rework once that pipeline exists.

New /api/v1/learning/timeline (per-verb first-success date + success
rate, parsed via the existing splitAction helper) and
/api/v1/learning/trend (30-day daily success/fail counts), both
read-only queries against executions. Patterns and skills sections
call the existing (untouched) ListPatterns/ListSkills endpoints and
render an explanatory empty state instead of nothing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/App.svelte

@@ -10,6 +10,7 @@
   import EntityDetail from './pages/EntityDetail.svelte'
   import Agent from './pages/Agent.svelte'
   import Knowledge from './pages/Knowledge.svelte'
+  import Learning from './pages/Learning.svelte'
   import Audit from './pages/Audit.svelte'
   import { newChat } from '$lib/stores/chat'
   import { summary, subscribeContext, openSignalCount } from '$lib/stores/context'
@@ -33,6 +34,7 @@
   import BotIcon from '@lucide/svelte/icons/bot'
   import SearchIcon from '@lucide/svelte/icons/search'
   import ScrollTextIcon from '@lucide/svelte/icons/scroll-text'
+  import TrendingUpIcon from '@lucide/svelte/icons/trending-up'
 
   let page = $state('chat')
   let routeParam = $state('')
@@ -71,6 +73,7 @@
     { id: 'events', label: 'Events', icon: ActivityIcon },
     { id: 'agent', label: 'Agent', icon: BotIcon },
     { id: 'knowledge', label: 'Knowledge', icon: SearchIcon },
+    { id: 'learning', label: 'Learning', icon: TrendingUpIcon },
     { id: 'audit', label: 'Audit', icon: ScrollTextIcon }
   ]
 </script>
@@ -210,6 +213,8 @@
         <Agent />
       {:else if page === 'knowledge'}
         <Knowledge />
+      {:else if page === 'learning'}
+        <Learning />
       {:else if page === 'audit'}
         <Audit />
       {:else}